You're on the right track, Steve, the larger carb and a less restrictive exhaust will allow your Ryobi to turn out some useful power.

I trimmed off the flywheel fins with a milling cutter in the drill press, after cutting most off with a hack saw. This allowed me to true up the center as well. You're gonna really hate yourself if you didn't keep your dad's drillpress, it's more than a bit handy for this conversion stuff.

By the way, keep everything you remove from the engine. I reused the choke assembly on the bigger carb (mine's a Tillotson), and I used the starter pawls, springs, and pins and recoil assembly to make up a starter.

My Ryobi is in a Balsa USA 1/4 scale Cub that I'll be flying for the first time this weekend. Keep your fingers crossed for me.

Have fun:
Allan