Re: oversize 41mm exhaust valves, aftermarket or genuine or custom valves
Depending as some aftermarket valves are made by the same company which make the originals from Ford. Go the better ones made out of Stainless Steel which are Swirl Polished, etc, etc. See if brands like Speed Pro, Manley, TRW, etc, etc make any off the shelf. I find standard head gear is good if you don't rev past 5500 prm and don't have more than 100 lb seat pressure and 250 lb open pressure on the springs !!!