G'day Trev,
how fast do you want to spend?
You could put in RR/SR valves in 67-0968 = 1.41" ex 67-0967 = 1.38" with a bit of seat and port work to run a 30/32mm carb. Bump the comp up to 8.5:1. Lighten the valve train components, balance everything, the list goes on and on.
Then you'll have to make it stop, more $.
Cheers