Probably my favorite “retro” AR-15 build comes from ar15.com poster and master AR builder John Thomas, and isn’t a faithful representation of any actual historical AR-15 at all. Rather, it’s a “what-if?” that John calls the “AR-14”:

The historical AR-14 was a civilian sporting rifle, but John’s AR-14 concept combines several early AR-15 and AR-10 features like the “can” compensator and brown furniture with a very 1950s-esque flattop upper receiver with a folding carry handle. The removal of much of the details on the firearms certainly help sell the rifle as a concept/very early prototype.