Kinda hard to picture what you're thinking here. Are you contemplating converting a non hybrid to a hybrid? The 01 was not built to be a hybrid. I've had a couple of that era Prius's, they're excellent cars. But a level of complication that you can't imagine.
Basically, a hybrid conversion is going to require that you pretty much gut the highlander. Replace the engine, the transmission, the axles, install a HV battery and a Aux battery in the rear. Massive wiring changes, computers (my old pri's had 7 computers!) And the HV batteries are not free (or even cheap.)
I bought an 07 Highlander a few weeks ago. I studied the awd, and the hybrid version. Gas mileage isn't much better and the complication factor is really something.
I settled for a base (Sport) with a 3.3 engine. I don't have to worry about the alternator/drive motor down on the output shaft of the trans or the motor on the right side of the trans, no inverter or inverter pump, no unconventional a/c, electrics, or brake booster pump. No huge battery behind the rear seat, no fan to keep the HV battery from overheating, and no little 12v battery in the left rear fender well. The real upside to the early hybrids was that the electronic systems really provide a boost in performance. I loved my 02 Prius! And mine was really reliable.
If you want an awd, hybrid Highlander, save up (or borrow) the nickles and dimes and buy one. Converting your 01 would be a long term nightmare and the outcome would be much less than satisfactory.