While it may not be a big issue, I'd be wary of any seller who didn't know exactly what (s)he was selling - the 4JB1 is the 2.8l diesel; the 4JG2 is the 3.1l model.

You will need the transmission (transfer is part of the transmission) from the same donor diesel. I would not buy just the engine as these transmissions are not easy to get in the US. Get both, you will save time and money.

At any rate, please see the link in my signature for a diary of sorts chronicling exactly the project you're proposing. My donor Trooper is an '88, but aside from a few minor wiring differences, they are the same vehicle (assuming yours is a 4-cylinder).

Let us know if you have further questions.