Best performance mods for a 20hp single cylinder briggs ic

I am wanting to build a racing mower with a murray wide body a peerless 700 transmission and a 20hp briggs single cylinder and was wondering what mods i need to do to the engine to be able to run high rpms safely without throwing a rod any advise is appreciated.

I am more experienced with flatheads but I'll give ya what I know. Port any rough casting in the head. Leave the intake slightly rough for good fuel atomization, but don't leave enough to disrupt flow. Exhaust should be smooth. Idk if performance cams are available for these vertical shaft singles, but some people weld material to the cam lobes to make them taller, then grind them smooth. I personally don't like this method but if you have the tools to do it and spare cams, it's worth a shot.
I think 20 horsepower is plenty geared right to be honest. You can "adjust" the governor or remove it altogether for more rpms, but over 5-5500 you're in the danger zone.

If anyone has any corrections to anything I have said, please feel free to correct me. I don't want to give false information by mistake

Thanks for the tips so 4500 rpms will be safe with stock rod and flywheel

Things don't necessarily just break at a specific rpm. Things get fatigued with time and eventually fail. I've heard some go kart racers that used 5hp briggs flatheads used to put in a new rod every three races. I would think it's hard to tell exactly what's going to fail when. Not only that, but you have to take into account imperfections in the parts too. It's possible to get a weak casting from the factory, like a rod with an air bubble maybe or something like that. So, depends on how much your going to use it at high rpm and if your willing to risk the engine. With billet rods and most of the other parts stock, you ought to be able run it pretty hard for just about as long as you want.