An inquiry has been made into the aluminum block weight ,price, availability. It's kind of hard not to use block that I have sitting here, all machined and ready to go. But then I need heed the advice I have given to others: just because you have something on hand doesn't mean you should use it. You can always sell it and use the funds to get something more suitable for the project.
Edit: the problem with that is I can never bring myself to sell Hemi stuff. So I wouldn't have the funds from selling the iron block, I'd be out the full cost of the aluminum block if I go that route.