Why am I drawn to the aluminum??

I've been planning a junkyard 5.9 Magnum in my 69 Dart, with plans to use the RHS heads from IMM.

I'm close to ordering heads and find that for whatever reason, I'm wanting the Edelbrock Performer RPMs.

One reason that makes some sense is weight reduction. I've added about 50 lb with Caddy CTS seats and can balance that out with the lighter heads. Really not that big a deal but not insignificant. Maybe it's just that aluminum is sexy :D

With the same parts, I think performance will be a wash. I'm planning an an air gap, 750 DP, and "a cam".
Power to the ground via 833 OD 4 spd with 8.8 410 gears, 27" rear tire - 285 40 18.

Trying to choose a cam hurts my brain. Brian at IMM had suggested a Thumpr. I don't want to get into a debate with the Thumpr haters but I think it would be a good match with either head.

Cost will be close enough between the two to be a non issue. I'll need rockers and pushrods either way. I found a local head shop that will go through the Eddies for a reasonable fee.

I had thought I'd need a piston change to make enough compression for the Eddies. Doing further research I think not. This is likely the key factor in my decision. Here's why I think I don't have to change them.

http://www.hotrod.com/techarticles/engine/hrdp_0804_small_block_mopar_engine/viewall.html

The Eddies made excellent power with stock pistons. However they do not give the details on compression ratios and I would not want to put all my faith in one article.

So I did what I could to gather more info. Here's what I came up with using my Mopar Engines reference, Google and the Summit compression calculator.

Some info was hard to track down. Stock piston dish volume and how far down in the bore they sit are not in the reference. Below deck height is listed anywhere from zero deck to .070 on forums. .050 is the most common spec given. I found nothing for dish volume.

Working backwards using .050 below deck, a factory .048 gasket, 62 cc chamber and factory 9.1 CR gives a 9 cc piston dish volume.

Eddie heads are 58 cc. Using a .028 gasket and 9 cc DV gets compression up to 9.87. A .010 head shave puts it up to 10.

Eddie states the head is good for up to .580 lift but warns that stock pistons may not have clearance depending on the cam. They specify a .042 gasket. The Thumpr cam has a modest .513 lift so some room to play with.

My gut says the Eddies could work out fine but I know I could be way off base with my calculations.

So like O'Reilly says, "tell me where I'm going wrong here".