Hey Rick,

If you want my opinion, here it is. If I had the engine sitting there, I would bolt it on and go fly the thing. The USL120 is so light that I don't think you will ever look back. If indeed the engine is only a couple of ounces heavier than mine, then even with the added tail weight I bet you will only be 3 or 4 oz. heaver than me. Mine absolutely floats around. As for the power, it will be a blast at times and you can pull the throttle back anytime you want....
I don't know what your plan is on the flap option, but I did install the flaps and am having fun playing with them.......I've only got 6 or 7 flights on mine so far...
You might consider reinforcing the firewall attachment points, and make sure on ground clearance for the prop.....
Also, there are a lot of guys running G26's on these birds.....I suspect they are much heavier than your 220. I believe their planes fly quite nicely even at their weight.

Just a bunch of my opinions!!!!

Jeff

p.s.- If you do decide to use the 220, keep me informed. I would like to hear how it turns out and maybe see some pics!!!!!