Aluminum vs. iron heads, I guess that's your primary question.
I'm not speaking from personal experience, and maybe that's a bad thing; but, from what I've read... aluminum heads are fairly hard to seal to the block with conventional head gaskets. Aluminum has a fairly high coefficient of expansion, so when it heats up it moves a lot in respect to iron, and when it cools down it does it again. Apparently all this squirming around on the block compromises the head gasket's abliity to hold a seal. and that is bad news.

Now, this from experience, aluminum corrodes like the dickens if you have anything less than straight antifreeze in the block. I messed up the water passages on a really nice smallblock Torker intake by running 50/50 water/antifreeze for less that a year, and that antifreeze was the good Prestone stuff.

I used to think, yeah man, I'm gonna build me a L-88 with the aluminum heads and all that good hardware. No iron head L--72 for me, I can't stand the extra 100? lbs on the front end of my already overweight 1/2 ton GMC. Well, I got over that after I grew up some, and decided to shave the weight elsewhere, as if it really mattered on a pickup. I just did not want the corrosion problems associated with aluminum, and ruining a set of aluminum heads is a lot more traumatic than ruining a manifold.

And now to that head gasket problem, about 5 years ago, I blew a head gasket on a 350 Chevy about 3 miles out of town. By the time I had shut it down, the head (iron) was cracked and the block was cracked in the same place. So a bad head gasket ruined a perfectly good 4-bolt main 350 block in about as much time as it took to write this paragraph. If this can happen with a mild iron-headed smallblock, it can certainly happen with a high-powered aluminum-headed big block. I simply would not take the chance of ruining a block from a head gasket failure if I could avoid it. If you're going to be on the street with your ride, I would strongly recommend iron heads, because I dont think you'll ever see a difference due to the extra weight. If you're gonna race it, and use the aluminum heads, I would retorque those babies after every run, and replace the head gaskets after every 10 runs. The only sure-fire way to seal aluminum heads to an iron block and have a worry free ride, is probably to o-ring the block, and that is indeed an expensive proposition.

Randy