I found a suitable replacement stud at Mc Master Carr for not too much $. Replaced all the copper nuts with new and tightened them until I met a sort of sudden large amount of resistance with a 3/8 inch ratchet. You will know when you get there. No need to overdo it. Also used Permatex Ultra Copper sealant--a thin film on both sides of the gasket surrounding both the intake and exhaust openings. So far no leaks. I had been seeing oil leakage from the intake openings due to blowby oil.
Peter