Bill-
This is probably a question for Steve, over at HondaTwins.
I think he might know, if anyone would.
I'm not sure if it could be done without some machine work.
The old 305/350 "kit" was actually just a big (12'th over) overbore, like guys do with the 450/500 conversion. I had it done on my own SuperHawk, back in The Day - I do recall there wasn't much meat left in the cylinders afterwards......
bill2