RE: help....
If you post some stats about your plane it would help us figure out where to begin.
- For starters, you can state the name/brand of the plane incase someone familiar with one
- The weight of the plane (if you don't have a scale, just say what the manual says)
- Maybe the wing surface area (sq. ft.)
- And if possible, wing loading oz. / sq. feet).
With that information, members here can get a better idea of what plane you're dealing with. Look around the forums and see if someone else doesn't have a similar/same plane as your's and see what setup they have. Is your plane by chance the Parkzone F-27 Stryker? If so, look in the Park Flyer forum for a thread dedicated to it
From limited personal experience, and just as a wild guess to start things off, taking into account the 480 motor and 7-cell pack you mentioned, I *think* you can try an Eflite 480 outrunner (I think the higher KV version puts out ~275-300 watts?) (do they make an inrunner version?) with an 11x7, 10x7 or 9x7.5 prop (APC brand) or (smaller prop if using a regular inrunner brushlessmotor) to give you the speed you would need assuming that the larger prop diameter clears your wings at the rear, at least 25 to 35 amp brushless speed control that can handle li-po's. I don't have experience with lipo batteries, but I know you'd want to get a 2 or 3-cell that can accordingly discharge 30 to 40 amps which will safely provide the said motor with enough amps, and be the right size/weight.
My suggestions may be waaaay off base, but I thought I'd share some info to get you pointed in the general direction.