Finally getting my brother in law to just go for it.
Stock exhaust port was only 15mm as compared to 40mm bore...stifling. He widened it to 22 and ovalized up to 1.5mm at peak. Top speed went from flats 16, to flats 21 With him riding. No other changes. Low speed grunt reduced proportionally to speed change.
Proma circuit pipe is enroute to offset the odds.