My 273 won't rev much past 4500 but I only have a Isky E-4 and I put it in a few degrees advanced. The bearing clearances are pretty tight too. My heads are similar except I didn't use hardened seats or stainless valves. Look on post 5 of my build thread. Mine needs more cam but I refuse to run headers so Ill stick with the stock manifolds and the HP single exhaust. tmm