jtairney,
2 stroke engines produce, in general, about 1.2 lbs thrust per cubic inch displacement. 4 strokes about 1.1. Your UCD 46 weighs about 6 lbs. The OS55 will produce about 1.2 x .55 = .66 lbs thrust. Not enough. You need at least a .7 cu inch 2 stroke or .8 cu inch 4 stroke. This is all very approximate but OK for picking components. There is very little difference in static thrust brand to brand for 2 strokes in the low cost types. I have flown my UCD 46 with a YS 63 which is about enough engine (supercharged). I now have an OS 91 4 stroke on it and that is more than just enough.
Something like a Tower 75 would be a budget engine that will put out the thrust. I don't know how good transition is. I run an OS 50 and OS 46 on 3d planes . They are fine for 4 lb planes and transition smoothly.

Why do they call it a UCD 46 when a .46 engine is too small? I guess they would say a .46 will fly it, just not 3d.