The Magnum ought to be a good choice, especially since you haven't let yours get fat like I did (I did several mods that added weight, as well as a few crash repairs over the last two years). I've got a .65 Saito in mine, plenty of go even with the weight.

ec121--what engine is in your Cub? Looks like a Saito, but haven't seen one with ribbed valve covers until you get to the 1.20, unless it's one of the much older .50's. Great job on the dummy. I took the 'road less travelled' and made my own dummy, took two weeks of fiddling.