they are all correct, absorb the suggestions, make an educated decision.
remember everything you do that gets you more costs more somewhere. performance = $+time

compression builds HorsePower but at the cost of needing higher grade fuel and a lot of other support upgrading expenses.

firstoff, if you dont touch the inside, the airbox is very restrictive and the exhaust is sub par. the carb is perfectly adequate. the rev limiter and secondary drive pinion gear are also a common issue.

changing the gearing, from the stock 33 tooth
changing the ignition modual to increase the RPM limit
changing the intake before the carb & removing the AIS
changing the exhaust.
all these things can be done without tearing the engine appart.

also going with HC pistons without also doing the valves & cam, intake, exhaust, ign., is leaving a lot out of the equasion