Compared to other racing venues I've been involved in, why not just make the boat weight have a minimum with driver, and not restrict the engine size? Would cover alot more than just aluminum blocks. Possibly could cover future Kevlar boats, ultra light unsafe boats, etc. Just hook up a scale, everyone has to weigh this, this is the engine size you're allowed, now go for it. Seems simpler to me, just my 2 cents. 

Bad form to require a promoter to have scales for one class that unfortunately is not that strong yet.  If you had so many boats you needed to qualify for the heats and if the class was nation wide then scales would not be that significant to the guys putting on the race.  (With that kind of interest it would be a professional event with things like prize money! What a concept...)

I think that opening up the rules is fine just be prepared for what you get. I would hope that if someone was so passionate about it they would put one together and test it to see if it's competitive.  Even if it didn't test well it would be a fun river boat. 

As far as the weight savings Alum. over Iron and assuming scales are not involved I'm sure that enough weight can be saved in a hull to make up the difference. ( read vac. bagged, Epoxy/Carbon/Kevlar). Have fun with this subject it's a good one.   

Shirl I know you know the small block & LS better than anyone and I figured if anyone would give it a shot it would be you.  Good luck, have fun. By the way does anyone on this site besides us old guys know what your "Eracer" means?