one of the problems with the 284-.528 is mopar performance's .028-.032 valve lash recommendations.. using .022 or .024 as a starting point will get the seat timing a lot closer to a real 284 degrees. this is probably a case of too high of a compression ratio for pump gas. also factor in the heat that cast manifolds run at, 700+F, and things can stack up. an asymetrical lobe camshaft is a benefit in reducing cylinder pressure. even if the pressure is reduced to 180psi there's no guarantee of smooth sailing. the tune up will be critical.