This is where I would start:
Swap the 4:11 gear for a 3:73 or maybe a 3:55, probably the 3:73s
You could try a taller rear tire to off set the gear but that would be experimental.
check the condition of the engine, compression test, timing, plugs, and carb. Speaking of the carb, it's likely kinda big, you can work with it if it is a vacuum secondary, the crutch here is you have no info on the cam so some of this is going to be a guessing game.
Another thing is going to be the heads, you need good heads, if a head swap can be done then plan a cam swap to better the combo.