I had no installation issues...
I built an O-360 for my 9A. @ 143kts gs, I'm averaging 7.2 gph. I had no installation issues and followed the guidelines mentioned in an earlier post.
Make sure you discuss the choice with Vetterman before you order.
My reason? We have access to ethanol free auto gas and given the lower octane, I installed 7.2 compression pistons which, according to Superior, delivers 168-172 hp. The O-360 is heavier than the O-320, but if you install a fp prop instead of a cs prop, the difference almost disappears.
Aside from the inherent difficulty of slowing down an airplane with a prop pitched for cruise, climb is generally 1550fpm at 3500 d/a with a full load of fuel and my skinny wife.