Iv ran an a500 in my 68 more door for a few years and love it. Did nothing to the floor and used all the shift/throttle linkage from the 904. Had to cut the driveshaft and redo the crossmember. I run 3.23 gears and usually get about 20 mpg driving 70-80 mph with a stock 318
So, you didn’t have to alter the upper part of the cross member like everyone says you have to? I’m building a 67 convertible and don’t really want to alter my upper part of the cross member if I don’t have to