If you have the motortrend app or I think you can see it on Amazon prime there was an oil pan test in the engine masters series. It was 40 some HP picked up with an oil pan change.
63 had more cam duration and lift. Better exhaust manifolds but hp numbers are probably with headers. 63 had single point distributor with vacume advance.
I started working at the Honda dealer in 1974 about a mile from the fish hatchery.
My brother had 73 Sportster and a 74 Superglide. Both bought in Sioux Falls.
I think I would have known about a dealership in the area.