Hi Bob, I am just north of livingston Montana. I have had quite a few flatheads and currently ride a 1937 84" stroker. I'd be happy to answer any questions about the old flatties if your looking for one. Shoot me a PM anytime
Stock Big twin flatheads have a scavenger pump that returns oil to a remote tank mounted behind the seat post (horseshoe shaped oil tank). Both sides of the gas tanks hold fuel. I beleive the 45 cu in flathead used one side for oil, one for gas
How hard is it to get replacement parts, is there a way to increase compression ratio. Are flathead 80 frame, fenders, gas tanks etc. unique or do they share parts with the knucklehead. Thank you for your time BOB
Harley-Davidson 80 Flathead Performance tips and speed secrets by Victory Library
As far as the other components you mentioned, frames are the same and I believe that the fenders are as well. But the gas tanks are shaped differently on underside. OEM pars are going to be expensive and may be hard to find, so keep that in mind.