48 " Miss America what powerplant to use
If you can keep the weight down there's no reason it shouldn't fly with a Speed 400 and gearbox on 7 cells. Use 600 mah nicads or go for 900 mah NiMH but add an eigth cell.
I'm surprised you needed a 15 on the powered version. 48 inches puts it right in the 1/2A Texaco size. Or perhaps you wanted the rocket like contest climb that the 15 would offer?
If you wish to duplicate the hot climb using electrics then I suspect you'd have to go for one of the hot brushless motors. But keep the battery pack fairly small and the runs short or it'll get way too heavy to thermal.