Nodak is the place to go for a correct A-1 lower. They have the flavors one would need. I used one on my Izzy clone with a colt A-1 upper and the match was perfect. My A-1 used an old A-1 style DPMS lower from the early 90's.

Colt upper, NDS lower (M16a1) with a 16" barrel. Rest was GI surplus. And the target weapon to clone.