Hey guys. I'm rebuilding my 396 and the heads had only umbrella seals on the valves. The valves don't have a second groove for o rings and the stems aren't machined for positive seals. Will just umbrellas on the valves be ok?
They'll be good enough especially for a stock motor. They have done the job well enough for many motors and thousands upon thousands of miles.
For high performance I personally would go to a positive seal.