To get it to all fit together, I reckon your custom ignition, pipes, carbs, heads and effective exhaust port height based on engine stroke, cylinder deck/base, con rod length and powervalve timing will all have massive effects on power delivery.

Therefore if not using YZ250 carb, heads, ignition and pipes then any direct comparison is meaningless.

If you are worried about ring life with big ports, could 1990's WR250 cylinder be used? Then locate a suitable road based piston to fit with harder rings, rather than soft ones that wear out quickly.

Just my opinion, Vincent
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NSRless again...