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Re: cast iron or aluminum heads?
The material (Aluminum or Iron) is not the primary factory in determining the performance characteristics of a head. It's all about port and chamber design. If the two heads you are looking at are the same physical design, they should perform about the same. Aluminum heads do tend to tolerate a little more compression than their iron counterparts. In theory the faster heat dissipation of aluminum heads may actually lower their output compared to identical iron heads. Most dyno testing does not find much difference based on just iron vs. aluminum though.
One thing in iron's favor is then the heads have the same thermal expansion as the block. This puts less stress on the head gaskets.
If you are not exceeding about .475" lift at the valves, Vortec heads are hard to beat. Sounds like you will need an intake manifold so the fact that Vortecs need a specific intake won't be much of an added expense if you were buying a new one.
I would not try for over about 375 flywheel HP with a 327 in a truck. It is easy to lose low end torque when getting too much HP from a smaller small block. Even at 375 HP it might be "soft" in everyday driving without adequate gearing.
Sounds like you have a good start. Putting parts on a good short block is the fun part of a build up
Kerry P
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