What to Budget Close
My advice regarding making a thirty year old cruiser into a sportsbike:
Presuming that you are doing most of the wrench work yourself, expect to put about
three thousand into the engine (pistons, cams, carbs, pipes, miscellaneous) and be pleased when it
turns out to be somewhat less. Expect to put about the same into more modern chassis parts: at a minimum some
"upside down" forks; dual calipers with at least four live pistons each; wheels with good rubber;
and various adaptors: rods and plates. Most anything from this millenium is good enough.
If it pleases you: tank and seat; other bits.
For this much in expense, expect the performance of a bike costing at least twice as much.
It won't beat the top sports bikes from Europe or Japanese fours, but it will be at least a match
for sports/cruisers displacing half again as much (or more). Imagine how the riders will feel
when you dust them.