Don't forget about the Dodge and DeSoto hemis. Sometimes they can be had much more reasonably. Plus, the Dodge Red Ram was made all the way up to 325 kyoobs and the DeSoto's largest was a 345. Nuthin wrong with either of those. I like the Dodge Red Ram Hemis because they are physically a lot smaller than the Chrysler engines and can fit places the Chryslers cannot. And don't think parts are not available. Cruise the HotHeads site sometime. Just somethin to think about.
Here's you a couple of decent deals.
http://www.ebay.com/itm/HEMI-331-Mo...Parts_Accessories&hash=item4170c4524a&vxp=mtr
I know you said Hemi, but check this out.
http://www.ebay.com/itm/1954-56-Dod...Parts_Accessories&hash=item4d096dfe18&vxp=mtr
It's a Super Red Ram poly. Look at them saw tooth valve covers. That would rock in a rat rod. Also, I am almost certain that like their Chrysler counterparts, the Dodge Hemi heads will bolt right on.