Good luck with repair without manifold removal. This was one of the first jobs I had to do on a new to me truck. Manifold removal was my only way, my studs were badly fused to the flange. I cut the studs off flush and drilled them out, then tapped for 3/8-16 studs. I think 5/16 was the stock size, so moving up to 3/8 may make removal 40 years from now easier. 😄
