The camel hums are usually the 461 or 462 heads, the only difference is that the 461 heads do NOT have the accessory holes. These heads can flow as good or better than some Vortec heads with a little work. If that's what I got, that's what I would run.
MAKE SURE YOU DRILL STEAM HOLES IN THE HEADS TO MATCH 400 GASKET.
I personally would just use a flat top piston with the 400 on 58cc heads. Better squish, predictable combustion and timing. And you would still be up there in compression ratio.
This part may start an argument: I would run water/alky injection to cool the intake and control detonation. You will be able to run 92 octane with quite a bit of timing on the flat tops. You can use a nitrous plate to spray the water/alky mix. (windshield washer fluid for cold weather works like a charm).
Aquamist makes a good kit.
OR- build it as a 377 and keep the big dome pistons. Your compression would come down slightly but your RPM range would go up. Remember, it's the low-mid RPMs under heavy load that breeds detonation. A 377 with a dual tunnel with a couple of 500's will scream with lots of cam and 1.6 rockers.