Believe it or not, alot of that "slag" really isn't slag. Overly burnt aluminum. I have a small electric furnace and being that I can control the temp I do get more aluminum out of the cans. These propane furnaces are really meant for brass, copper, mild steel, and cast iron.
I wish I had the resources you have. Just that metal you made the body out of would cost me $300 here. All your supplies in general, probably around $1200. Nice build, wish I could make one.
Hey Rick, I know you know metal better then most but I have heard of guys getting burned BAD (one went blind!) From melting cans due to moisture in the cans from beer or soda. I would ABSOLUTELY ware a face shield!