Sounds like the old hot-rodder maxim--there's no replacement for cubic displacement. The Senior is designed to fly on a .46 2-stroke. My recommendation for plenty of power would be a .56 or .65 Saito (I love Saitos) or a comparable Magnum or OS and a 12-6 for the .56 or a 13-6 or -7 for the .65. You'll be surprised how little power the Senior will fly on. The smaller engines should balance well, and you'll save a few bucks on the engine, if you haven't already bought and run the .91.

I use a .56 on a Rascal 40, which is about the same weight as the Senior, has the same wingspan but a little less wing area, and it will do almost everything but hang on the prop. I use a .65 on a 9-1/2 pound 1/5 scale L-4 and it flies at 1/3 throttle. Plus the spinner you asked about earlier, you'll have a nice flying Kadet.