I had an old can of "Testors 1265 Olive Drab Flat Spray Enamel" I've had several years. After a few minutes of shaking, it sprayed well enough for a few light coats, and it looks like a perfect match. Another can is on order and that should finish it up.
Photos include initial first light coats the Testors OD Flat that I that look very good. The first can is getting low and I don't want it to spit so I have another small can of the same stuff on order.
The independent square paint swatch is the ANA 611 that was ordered for comparison. It isn't very accurate compared to its online example that was offered.
The first coats of the Testors OD will be lightly sanded and given one or two finish coats and cured. Then the receivers can be assembled, after I find a Colt full-length buffer tube and spring.
The last couple photos are a handguard and stock of an original USAF 601 a friend took for me. I t appears the Testors OD enamel model paint a perfect match.
The Brownells 601/602 dimpled front pin came it the mail and fits perfectly. That only leaves a safe/selector switch to be drilled and fitted to add the correct period detail hardware.