I will post a pic and video of the final product that comes as a result of this thread.
 

Congrats sir.
Dlo boxes aren't what I would call collectors items. They're wanted for the factory guts capability which you could replace if you ever decide to sell and someobe looking for a box will want to move them back and forth betwern hosts. You can also reparkerize the box to give it a clean finish (I did with my lafrance box) so in my opinion shoot it and run it.
The only guns I would want unfired and kept pristine are full factory guns like mp5s, converted hk94s and sp89s, etc.
If you already have an ambi lower with a sear I'd leave the box as is. You can always go ambi later but you can't go back. If you ever decide to sell see what the markets asking for either, and if the ambis are easier to see them do the swap them. Besides, sef are easier to swap out ejectors.
I'm jealous that you got two. May I ask the price range for those boxes? Curious what the market is going for.

Forgot to mention,
I can't think of any rare mp5s that would be desirable besides the newer FFDE Ral 8000 that is the hotness. Most smiths should be able to replicate that color however so the issue is finding a french parts kit. Do you have the SD and 10mm variants covered?

I'd think something more fun and worthy would be one of the K beltfeds such as the mm21ek. I enjoy good precision shooting but for fun factor nothing beats a good beltfed as I'm sure you already know. If you go that route, make sure to get rails added so you can add peq15s and load a beltfull of tracers and nvg for nighttime fun shooting off the hip.
Also, I'd suggest getting some cans for the MP5ss, specifically the knights armament ones as those ARE the most desirable and were used by scuba ninjas. Hkpro teufelhund Tactical has a group buy going on for those which I suggest getting in on. You will get your money back on those if you ever decide to sell.
Don't forget to get different locking pieces for suppressed shooting. Cans will increase recoil and can batter the receiver of you're using stock LPs.

IMO, unused has no real value for a registered box other than assuring it's in really, really good condition.

You've got all the cool toys...

I can't really comment on the unused DLO.  Frankly, I'm not nearly qualified to render an opinion on it as a still somewhat novice HK guy and collector.  It is pretty neat to see one in that condition though.

I will offer this.  I bought my Fleming sear last year and most people who looked at it think it was brand new.  It never crossed my mind to just keep it like that and not install it.  If I had a few of them, I guess I might have looked into it a bit further.  But I knew I was only able to afford one and that I was definitely going to shoot it.

I'm not sure what to tell you about the mp5 host.  If you have them all, I assume you have the N, SD, and K, plus one or more in 9mm, .40, 10mm, and maybe even the rare .45.  Beyond that, I haven't a clue what to advise you to get as far as that's concerned.  

I continue to envy your collection haha

I would personally leave them as SEF boxes myself, As other have mentioned there isn't a huge premium on a "new" vs. "used" HK box, so I would definitely shoot it.

Keep in mind that not every DLO SEF box can be legally converted to ambi.   One of the processes to have an SEF converted to Ambi is that the selector axle hole has to be enlarged.

Some of the DLO boxes have their engraving right up to the SEF selector hole, which basically means you cant enlarge the selector hole without running afoul of damaging the original manufacturer markings.

I cant 100% tell on your new box if it could be converted due to the red covering but the placement of the DLO markings look like the T in "CT" is going to run really close to the selector axle hole.  If you do send it off you need to be extremely clear with the smith that they should not damage the factory engraving in order to enlarge the hole.

I would definitely shoot the new DLO frame. There is really no significant premium on a new frame over a used frame. And life is too short to own guns you never shoot. I bought my DLO frame new directly from Doug Oefinger and immediately broke its cherry the moment it arrived at my dealer (well, after I had installed all the internals). I gave serious thought to converting my frame to ambi back around 2006 and am very glad I did not. You already have ambi packs covered with your sears. Use the ambi sear lowers when you want ambi and keep the DLO frames as SEF.

Thanks for the advice gentlemen. Based on your wise advice, I shall shoot the unused box, and I will not be cutting one of the boxes (one box has a SN that goes up to the hole and one is far from the hole).


I looked up the FFDE RAL 8000, and that's the exact model I've been wanting to make. I don't think HK parts has the kit yet.






Here is a pic of it (not my pic, I think it is a stock pic). Very cool. I do not have this version.











 

I contacted someone a while ago about getting the front rail on that gun.  Wasn't cheap, but it was available.

Maybe one day HK will embrace the civilian market.

David, was the front rail a factory HK part? Or was it made aftermarket? What was the price?

It has an HK part number, so I have to assume it could be made by them.  The rail was about $300 and would take 6 months to get.

I went through John Flagg at GMP Parts, who put in an enquiry through to HK Commercial sales here in the US.  It took them a while to track it down having to contact their German counterparts, but they found it.

The part number you're looking for is:  HKI/HKD     226210


There's a top picatiny rail as well on some of those guns, which I also managed to track down and get a part number for.  What I wasn't able to find out was where to get one of those trigger pack housings in RAL8000.  Sure you could have one cerakoted, but that will cover the selector markings.  I'm sure they have those colored housings available, I'm just not sure how to get one.