I'm a little hazy on special heads for the late motors (I'll have to re-read the Santucci Power manual!) The Kirby/Sissell heads are aluminum alloy but not of crossflow design like the older Wayne versions for the GMCs and early Chevs. I'm not sure about the Duggan.
The only late motor crossflow design I can swear to is the one-off types welded up from 2 V8 heads. These have only been done in cast iron, as far as I know, but I could be wrong here. Anybody with the true info, please post!