Lots!
Soundproofing (everywhere + fire proof foam soundproofing in the engine bay)
Replacing plastic body filler with steel seems a popular upgrade (fingers crossed you don’t have hidden rot)
Wiring as above plus fire extinguisher.
A fuel filter that sits outside of the engine compartment and modern ethanol resistant hoses
Convex door mirrors
Sticky backed card table foam on Westy louver windows to stop rattles
Best thing is to make sure it drives and stops like it should do. Gears should move easily, braking should not pull to one side or another, engine should be slow but equally “powerful” through the rev range, steering should have no dead spots or slack.
Priory?
1 Fuel lines and filter
2 get it running like it should
Big spend upgrades I wish I’d done earlier?
Bigger better engine
Gearbox final drive change to suit engine
Litesteer
Things i needn’t have bothered with….
Radio and subwoofer.