well unless you are capable of rebuilding the engine yourself, another engine is the easiest way forward, The engine WILL have to come out whitchever method you choose, as for the gearbox, it is much easier to lift with the gearbox atatched, assuming you have some lifting equipment, if not hire a hydraulic lifting hoist on wheels as it is then a doddle to remove it, i say leave gearbox on, as the drive shafts will have to be popped out of the diff anyway,
there are plenty of these engines on E/Bay ranging from �50.00 to �300.00 some are still in the doner vehicle, so you can hear them running,
it sounds a big job, but once you have the lifting equipment and( if you are not competent at this ) a haynes manual or similar, it is really straight forward, the thing to do, is , as you undo something ie wiring ,get some masking tape and lable it so that you know where to refit it.
Good luck, have a go you have nothing to lose now,