The ring groove widening was due to the prohibitive $$ for KZ650 rings.
The CB750 +1mm rings were $50 for 4 sets.
Compared to $75 PER set. A full set for 4 pistons was quoted to me (with tax) at just under $325.00.
So me being able to adapt to cb750 rings was a massive advantage IMO.
The only thing I think I MIGHT do past what has been done is add some oil weep holes.
All the cb750/550/650 (overbore and stockers) have more oil drain holes than these KZ650 pistons do.(in/below the 3rd ring groove)
But I dunno, the KZ has 5 in each side in the ring land area.
the CB pistons have had 4 in each side of the ring land, with 3 holes(offset from the set of 4 in the ring land) on the bevel just below the 3rd ring.
But also the KZ pistons have more of a wrist pin offset as well.
Perhaps I am worrying about nothing, they were designed well, just slightly different?
And prohibitive as far as $$ for shipping the cylinders....
That depends on how big/deep your pockets are.
Might be cheaper to have yours done locally.
I do have a set bored(not honed yet) if seriously interested though.
Gotta go slave away. Just checking in for a few minutes
l8r