Couple months back, after nearly waiting a year, I finally was approved for this.

The furniture is all vintage and I'd like to keep it that way. So, I'm going to get a different upper and stock to actually shoot it. I know there are differences between these and ARs. What kind of upper will work on this? That is, what do I need to look out for and what not to get.

Thank you.

First, congratulations on an awesome new MG! That exact M16 was my first MG back in 2002.

That’s a factory Colt M16. Any milspec upper with a fullauto bolt carrier will work. It’s plug and play.

I’d stick to top tier uppers and bolt groups. Don’t cheap out on any components you’ll be using on this lovely factory MG.

OOPS

Very Nice.

I have a Colt M16A1.
If I were you, it they are original to the rifle, I would pack away the upper, bolt, buffer, and spring, and replace them.

I recently built an upper using a Colt A2 upper receiver, Brownell's 20 inch 1/7 twist pencil barrel with chrome lining, NiB coated BCG, A1 handguards, and a Kynshot Hydraulic buffer.
Wouldn't skip the chrome lining if you want the barrel to last.
And the 20 inch barrel makes for easier to control rate of fire on full auto than a 16" or even a 16" mid length.
The hydraulic buffer really tames the recoil.
Doesn't eliminate it, as that would violate Isaac Newton's Universal Laws of Motion, but it does spread out the recoil and makes it much easier to hold your target.
Also slows down rate of fire without being "choppy".

RCA

To be somewhat pedantic, that is only partially correct.  A hydraulic buffer does, in fact, eliminate some of the kinetic energy of the firearm recoil by converting some of the kinetic energy of the moving bolt/carrier, buffer, and recoil spring assemblies into heat thereby maintaining, not violating, Isaac Newton's Universal Laws of Motion.  The coulombic damping of the hydraulic fluid as it is forced through orifices (aka ports) provides the "softening" effect.

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Best of luck.
MHO, YMMV, etc.  Be well.

mind sharing if this was private or dealer sale & what you paid?

feel free to pm if you prefer.

I built out retro semi guns with the uppers and furniture from my transferable Colts.

Personally, the carbine configuration is the most versatile.  I would (and did) install a Colt or LMT carbine receiver extension, h2 or h3 buffer, and standard carbine action spring. Add a Geissele SSF trigger.

Be careful about using KNS non-rotating FCG pins, as the support arms on the outside of the receiver will slightly burnish the anodizing.

Then buy top tier uppers and components. Again, don’t cheap out. Some genuine Colt uppers are a must: 6933, m4a1 socom, 6943, mk18.

I love me a 10.5” barrel in full auto, loud as hell but a blast to shoot. Don’t forget to pick up a 100 rd drum mag :)

Thanks everyone. I have my answer. Appreciate you.

It was a dealer sale.

I had the opportunity to slap my Mk18 upper onto a postie a few weeks ago at a private range. It was an absolute hoot. It is suppressed and was a good time indeed. Hoping to take my A2 upper if another opportunity comes along.


Someday...