CY engines are very close, might work well...
I converted a 26 with a full circle crank..Boutht a short block, removed excess material from the case, put EI and a prop hub on it, didn't run any better than a Stock G26...The larger ones might...
I have a new G26 PUH heli version engine here...It has been ported, balanced and otherwise made to work better than a stocker in a helicopter...Put a prop hub on it and ran it...Ran the same as a stock G26..9000 rpm, Mejzlik 18-6....I'm sure it will be better in the helicopter at 12,000 rpm, but the stock G26PU airplane engine is just as good in an airplane....
The grass is always greener on the other side