You could go further on the exhaust provided you change the blow-down value and alter the transfer height.
I run around 76-78degrees on a 350 twin, 4 / 5 mm on the exhaust from stock and a lift on the 2 forward transfers of 1.5mm but extensive cutting of the liner lower is needed to optimise the transfer volumes. Works a treat - masses of low down grunt, huge midrange and top end. The motor effectively has no real powerband as such. The concensus from the 'in the know' community was that it wouldn't run.... however, the reality is something quite different. Dead right about the polishing - waste of time. Matching the port end to the pipe works well on older, crude strokers bus can't say on the H-Honda !
Mind you, there's bound to be useful gains from matching the barrel to each crank case and working the transfer lowers etc..
There's my 10p's worth
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