Colt use to make a 7.62X39 ( if you can find one here )
Model 1, DPMS , Oly , Sabre , Armalite
You can always just get a barrel ( DPMS barrel is pretty inexensive through Midway )
The MGI bolt seems to be the best of the bunch. I have had a DPMS bolt go for over 2K without a problem but others have had issues with bolt breakage
Depnding on your trigger assembly, some Com Bloc ammo requires a firing pin and / or bolt mod to be 100% reliable. My CM single stage had issues
The C-Products are the current mag of choice but you would be suprised how reliable 5 rds work in a regular AR mag. I currently use 5rd 6.5 Grendel mags (C-Products ) that run like a top
Although I typically run non corrosive ( stash is getting low ! ), I don't get too excited running corrosive . A new gas tube is $15 , the bolt and carrier comes out easy for cleaning and its pretty easy cleaning the upper. If I have to spend $200 after a few years replacing a gas tube and a stripped upper I won't loose sleep