I am building a NORRA early Bronco and have the body off the frame so running fuel and transmission hard line on top of the frame rails to keep them out of harms way and out of the exhaust heat. I only had enough hard stainless steel line to run one length for the main fuel supply from the rear cross member. I had 25' of aluminum hard line on hand and used that for a return line for fuel (future EFI and redundancy) and ran two lines to the rear of the frame for the transmission cooler. The aluminum line is of course much more fragile than the steel line. I have been rethinking it's use and just wanted to see what everyones opinion was on using aluminum vs steel/stainless steel. My budget is tight and was trying to use what i had on hand but now thinking twice about it since i have access.