Performance engine parts are rare and expensive (capital E).
Better to leave the engine stock and concentrate on other areas.
Quality suspension components and lighter wheels are a good buy, plus trying to shed excess weight.
The cost of goodies for this bike can add up quickly over time.
Don't ask me how I know, and I did all this on a budget and was lucky to find parts being sold at the time.
Right time, right place. Which seems to have mostly dried up these days.
Even then, there was no way I could afford any internal engine mods, that's why I bought my engine years ago off a racer who retired his bike and parted it out.
He put $10,000 in the engine alone, which was way beyond my pocket book.
I'm not going to race it, so it will live as a fun play bike on the streets, so it should last a long time.
I have some key HRC parts stashed away, but even then, if any major component will need replacement in the future, that will be it.
I have the original engine, and can swap it back at any time.