I got to wondering just what the limit is for these heads? Lets allow a high lift (.680 if it will fit?) solid roller cam, lng valves and 1.7 rockers, tunnelram, 14/1 compression, 408 cubes, vacuum pump, thin rings, a center weighted crank to give some life to the stock block, added bottom end support of some kind, fully ported EQ318b heads, build the short block with as light a rotating assembly as is reasonable. My guess would be 675 hp.