The heads are fine for 400 HP. They're not bad "out of the box". You might want to consider better valves and springs. If using a mild hydraulic cam, they'll be fine.
100% agreed, DUMP the balancer! 2 Chevys, one Pontiac and Ford, all "bye-bye". Pioneer offers a very good SFI balancer for reasonable money, made in Australia, not China.
I say again, for the heavy car, build the 400... (:-