It's a tough sell and I know I'm gonna turn a lot of worlds upside down but here goes--
Iron makes more power-EVERYTIME. Iron is more stable. <<<Read this over and over until it clicks.
Seats move in aluminum and must be re-seated after some hard use (cycles). Valvetrain motion is translated more accurately ( refer back to stability comment) . Iron doesn't wick chamber heat (which is HP) out nearly as fast as Al. When you torque even the headbolts down the "click" on the wrench is "positive". It's hard to explain but Iron is the superior medium for heads and everyone looks at you like you're crazy when you say it out loud. The one and only benefit of aluminum is repairability-it can be welded. J.Rob