I have an electric xrt800 utility vehicle that I use around our property. There looks to be almost enough room for a Tesla electric motor, although it would probably mean raising the flat bed (or removing it entirely). The primary issue would probably be the actual power source; there's no way to fit a Tesla battery pack and my XRT batteries output only 48v.
Oh, one other problem: the xrt curb weight without batteries is ~1,000lbs IIRC so fitting a Tesla motor with a suitable power supply would be a pretty wild ride (assuming you didn't become a candidate for the Darwin Awards).