Which model 70 was ued as a sniper rifle in Vietnam? I have a chance to buy a couple model of 70's(both pre 64, both 30-06)).

Pre 64,with medium heavy target barrel and Unertl 8x or 10 x (not as common) scope.Medium target barrel is 24 inches long,flat target crown and and muzzle diameter is 0.790.This is the USMC version we commonly see in pics of Hathcock and Gundersen,,altho other versions with standard barrels were used as well.US was lacking on sniping equipment as usual when we went to WW2,Korea,and Nam,,we always had to play "catch up" so many off the shelf items were used.
Army used some M70s with the Redfield (3x9x) scopes as well,thhe precurser to the Redfield AR-TEL,and possibly the AR-TEL as well.
There was also a commercial Jap made scope used.It was NOT a USMC contracted item, It was called the "marine sniper scope",just a name,,not specific to the USMC from what I understand,have not researched this one much.
Pic up some of Seniches books for great reads and info.

Here are the three I have to choose from, and all I have for info is the single picture of each. The first one is an XTR. I think all of these have the thin barrels(I could be wrong).

Bottom one is a featherweight,so toss that one out.The other 2 appear to be standard barrels,but top one appears to be a "supergrade",toss that one out as well.Middle one may be ok,but you definitly want more info.Most of the snipers did not have the raised comb,,,but some did.Hopefully LongTrang and Hal143 will jump in and add.But if left in that configuration (middle one) that would be an example of an "off the shelf" pressed into service rifle.

Yep...I'd go with the middle rifle and re-barrel to a Target barrel.  If it's a pre-64.  Depending on the year, it may or may not have a clipped receiver.  Not a big deal but some guys prefer it.
I'd also convert only if it's a standard, non-rare variation rifle.  You might not want to convert a nice rare super-grade or something and ruin a valuable piece.

I'm building my own from scratch.  I have all the correct parts, just waiting on the Unertl .......and someone to barrel it up for me.

You can use the Standard stock or the target stock.  Many guys prefered the standard stock, so the only big ticket item needed is the Target barrel and Scope. The standard stock barrel channel will need to be opened up to fit the Target barrel profile.  Douglas target contour barrels would be a suitable option if you can not find the real Winchester barrel.

Top and bottom rifles are post 1964 guns. The middle rifle is pre 64 would be a good starting point. You could salvage the action and the stock. The closest model to the sniper rifle was the varmint version (the biggest caliber I've seen in this version was a short action .243). Barrel change, stock inletted for the correct diameter barrel and bedded, action clip slotted. And, of course the correct scope-an 8X Unertl. There used to be a guy that advertised Model 70 parts in the small ads in the back of GunList. Shilen could replicate the barrel for you in the correct countour. length and weight. All in all would make a nice rifle, but it ain't gonna be cheap.

This is my clone,using a 10X unertl,,I can't swing $4-5 K for an original MC marked 8x scope.Note how massive the "medium heavy" target barrel is,this is an original winny barrel.

Well with my humble experience this is what I see.  The top is a post 64 M70.  It's a no go.  Your bottom one is a post 64 featherweight as M1 Sniper pointed out.  It is also a no go.  The middle one is the go to rifle.  However from your picture it appears to be a pre 64 super grade.  The stock combs are a characteristic of these guns.  I would NOT convert that rifle.  It is worth so much more in it's current configuration that it would be a travesty to break it up.  It even appears to have a receiver target sight.  Ideally you will want a pre war pre 64 with the clip charger slot and clover leaf tang.  Some say this is optional but all my research and photos indicate that USMC snipers fielded the majority of M70's with these options.  You can also find spade tang, clip slotted receivers as well.  It all depends on how accurate you want your clone.  Sky is the limit if you got the funds.  Original Winchester M70 target barrels are RARE animals.  The ones you will find will be expensive.  Douglas is a good option.  They also made USMC M70 replacement barrels so it will be accurate.  As far as stocks go the Corps converted standard rifle stocks, used target stocks (though less common) and even more rare a super grade type with a comb.  On a side note...USMC did press into service standard M70 hunting rifles though scarce.  So that could be another option if you desire.

Personally I would scour the pawn shops and look for a good donor rifle.  That way your not breaking apart valuable rifles. Remember, Winchester no longer makes the M70.  So any M70 is great shape is commanding high prices these days.  Especially unmolested Pre 64's.

Edit:  Forgot to mention this; the caliber MUST be 30-'06!!!

Thanks fellas, I don't own any "normal" rifles, just military and my knowlege of civilian arms is very small. M1sniper, I love the looks of that rifle, I really want one! I wish I would have kept the Unertl scope I sold last year though, It would have given me a better start.

My rifle turns out to be,I hate to say rare,so I'll say unique.The sn according to Roger Rules book falls into a block that was "unrecorded" by Winchester as the receiver was made during WW2 when commercial firearms were aahhh regulated for sake of a better word.Hal and I have concluded it was made sometime late 1945/early 46.But it has all the "pre war" (pre WW2) characteristics.Bolt,safety,receiver bridge etc.It has the cloverleaf tang,and has the stripper clip guide (clip slot).
The stock I won off GB,,,and you guys think finding a minty 601 or original car stock is hard and expensive?? Try finding a miny pre 64,pre war M70 wood stock void of any hairline cracks,chips or other damage.Wheeew,mind boggling.This one had no splits,cracks but does have a few dings I can live with,and the color has the nice military red/brown look to it.
If you can get your hands on any of Seniches sniper books and a copy of Roger Rules Winchester book,you will see just how many variations there are and can sort out what you need.I got extremely lucky on this one,I ONLY had to hunt down the stock and scope.Rest of rifle came to me complete,,from a very well edjucated member here.

I'll second that on what M1 says about pre-war / pre-64 stocks.  They are a booger to find in good shape and at a reasonable price.  I had to buy 4 to find a really nice un-molested one.  It's a killer stock but ran me $400.  But I also took a gamble on a really cruddy looking stock nobody wanted for $65 and it's pretty darn nice as well.

Many sellers can't see hairline cracks or they don't want to see them.  So it can be a gamble sight unseen.

M1 turned me on to a seller with a New unfired NOS Pre-64 Winchester target barrel in 30.06 for $400 as well.  I'm scared to even look at it, it's so clean.  Now I'm into it for $800 in just the stock and barrel alone.  I would have prefered used-not abused parts, but finding lightly used unmolested parts has been tough.

I recommend getting a spare stock.  A hot load or a drop on the floor can split 50 year old wood when ya least expect it.