Hi Phil...
My old 500/4 SOHC Honda race engine used Kawasaki pistons....
The gudgeon pin holes were 2mm smaller and had to be re-machined and the valve recesses recut 0.5mm deeper, then they were perfect....plus a 1.5 raise in compression.
Worked well with the Joy (Isle of Man profile) cam and the close ratio box.
If I remember rightly the dyno-read-out (still got it somewhere) was 71bhp ATBW
So there's always "something" out there, its just a question of satisfying the compliance police
