A lot of g bodies came with Chevrolet 350’s not Oldsmobile
So you have to make sure they’re for an Oldsmobile 350 engine
Most likely any header from a small block Oldsmobile car should fit in
A c10
Yes a ford roller rocker will fit the 350
For a mild engine I recommend comp cams magnum
1441-kit roller rocker kit for small block olds, available at jegs
https://www.compcams.com/catalogsear...Category_Code=