cast iron heads vs aluminum for stroked 340

Well, I hate to rain on your parade, but What you are doing, many would consider very dangerous. Putting that much power in a soft chassis, is a recipe for disaster.
Far better it would be to put any old 360/4bbl in it and work the kinks out of the suspension,steering and brakes,etc. first. Get the tubs in,tired,geared,and certified.Then, when its finally reasonably safe, you can drop in that monster.
Besides, a torquey 360 in an early A is a lot of fun all by itself.

just saying.