Thanks fellas, I finally managed to wrestle the thing in there; guide pins definitely help. I also found a dual sling setup made from 2 ratchet straps (one at the bellhousing and the other through the shifter hole ) gave me the right kind of support to get everything in line.

Of course, now I find that the output shaft flange on the new unit is shorter than the old one, leaving me shy of the driveline. It looks like just swapping the flange ought to do the trick. assuming that the shafts are the same.