I'm pretty sure (through the haze of maiden flight nerves) that the problem with "going to fast" was simply that I didn't trust going to idle. I do remember that the model dropped quickly when I cut power so landings have to be power-on then cut just before touchdown. I'll do a little more stand testing of the 72 then put it back in. It's impossible to fine tune an engine until it's in a model connected to a throttle servo and Tx.

I hadn't heard the idle of adding diameter and pitch for equivalent props. That's a pretty nifty rule of thumb.

One good bit of news is the mounting holes for the Saito 56 (that I have in my Cub ARF) and the ones on both the Saito 72 and 82 are EXACTLY the same. The larger engines weight about 50g more but that's not a major problem.