This would be my idea of retro AR's. I know they all have the large pin, but I don't intend on swapping uppers anyway.
First is left and right view of an SP1, R6000, c. 1979. Next is a early Sporter Match HBAR, R6601, c. 1991 with slick side

, and a Govt Model, R6550, c. 1988, also with slick side. Don't you just love the way Colt uses what they have on hand?