I think i'd stick with the 406" setup, it's a lot easier. You'll need a .900 BS or smaller cam, somewhere between .630 and .650 lift on 106 lobe C/L solid roller. The Dart steel heads make good power and are cheap by comparision, 1 7/8" headers. I have 2 also 1 is a 4 bolt the other is a 2 bolt. I fill them to the bottom of the water pump, studded both. I go one step further. I tap the steam holes and put 1/16" pipe plugs in them, this helps keep the bolt holes from cracking to the steam holes. 650 is fairly easy to reach with a 406" motor with a good tune up.
JMO
Zip.