Burned exhaust valves are sometimes the result of one too many valve jobs, in my experience. There needs to be a "margin" at the edge of the valve that's about 1/16" or more. If the valve gets ground to a knife edge the heat of the exhaust gas going past it several times a second will cause the valve to curl up, leak, and burn. Fortunately, 235 exhaust valves are the same size and length as small block V8 exhausts, and stainless steel valves are plentiful and dirt cheap. If you are willing to do a little pocket porting and valve seat grinding, a 1.6" small block exhaust valve can be fitted to the stovebolt head.
Jerry
