Need help with unknown upper

[SLYoteBoy]

Hey all , my dad purchased a larue quick connect scope mount (the one with the throw levers) and its picatinny rail style. The current flat top on his AR is weaver style , it is held on top by two lugs with roll pins and 3 evenly spaced screws , and 1 closer spacing towards the charging handle (4 screws total) as looking from the top. I havent payed attention to other AR's , but im guessing there all forged from one peice. He wants to know how and if he can get a picatinny flattop peice , like are they standard or to each maker there own? pics later when i find a camera. thank you