Hey, I'm glad to try to help. I know how it is to try to finish a model you're not sure what it is and, besides, I enjoy a good mystery! I was originally thinking it was a Great Planes model but gear doesn't match up. I also thought it might be a Nitroplanes model but I can't find any good photos or instruction book to compare. I wrote their customer service folks asking if they had a digital copy of the manual this morning: we'll see if they reply back. I haven't seen any with that graphic like your plane has yet from any manufacturer. But someone could have recovered it or maybe it was a small run in that scheme or maybe it's an obscure manufacturer, I don't know...

I can't help you much with motor size. Maybe somebody else can chime in on that. It's at least what I would have called in 60-size plane back in the nitro days but I could be wrong about that. Anyway, I'll keep trying to look and maybe we'll get lucky. It would be nice if someone here would recognize it as a plane they had built before but I guess that would be too easy! The mystery deepens...

https://www.nitroplanes.com/j3pipercubs.html