You will need one of PSA's uppers for sure. Here is a link to a recoil system that will work. If you don't want a carbine stock buy the fixed stock.
https://www.armalite.com/SearchForm.aspx?search=308 receiver extension&exclude=&mode=store&index=0&size=20&searchtype=0
Get a good barrel and BCG.
The PSA pivot pin and take down pin are their own length. On my pistol I used someone else's pins and they are just a tad long.
I have 2 PSA's. One I built and one they built. The one they built has a bunch of different parts now.
Good luck and have fun.