I did a semi retro A2 build. I used a surplus A2 stripped upper. I didn't go so far retro that I used a correct lower and all that. Stripped A2 surplus upper, stripped PSA lower, Green Mountain 20" A2 profile barrel, round handguards, A2 full stock. It's not the rifle that anybody here would build as a competition rifle, but I really like it. I'll build a correct A1 sometime. I'm sure I'm in the minority but I like the look of the triangle handguards on an A1/A2. I would have used them when I built my A2 but the round were what I found when I looked.
I've used PSA LPKs. I haven't had any problems with the parts except the triggers suck. Really, they're bad. I'd have no qualms about using a PSA LPK and an upgraded trigger group. I have a Geissele in mine. If I was building a rifle that I was literally going to go into battle with, I'd probably use a little better LPK but the PSA LPKs haven't failed me yet.