Congrats on the Hemi!!! As far as weight.. they are a bit beefey. Running the blower you get rid of the cast iron intake and the whole front cover and water pump so you shed a lot of pounds. On the other hand you add almost 100 pounds of blower, manifold, and carbs. Hot heads has the conversion front cover so you can use the Chev water pump which is availablel in alumininum. You could use a mag blower but pay a bit more for it. I don't remember what the weight difference is, 10-15 pounds for mag blower and manifold maybe a bit more. They do polish a bit different color but pleasing.
If you can I'd go for the aluminum heads. They old stuff is probably pretty well used up and will cost a lot to rebuild and replace. You can save significat weight here too plus get a better part. If I recall the iron heads weigh about 100 pounds each complete. Alum are probably half that.
Don't forget the headers. 2" headers and collectors can get pretty heavy fast.

A good buddy of mine just got what he though was a 392 but it turns out is is a 331 industrial with the gear drive cam. Kinda an orphan but I think Hot Hemi has the conversion stuff he needs.

I really wish I could afford one for my 41 Willys.

Good luck.