My son and I used to get frustrated trying to put the driveshafts back in the race cars, and we pull the engine/trans several times thru the summer. We'd tried several different ways of reinserting the driveshaft into the trans but none was a sure-shot first-time affair. Finally Brad (the son) says, "Why don't we just pause as the engine/trans goes in and insert the driveshaft by reaching through the shifter opening?" So we tried it and that is the way we do it now. Quick and easy! And one does not even have to disconnect the rear end of the driveshaft.
The only caution is to NOT have much force to the rear applied to the engine as you insert the driveshaft!! If you do, the trans can come to the rear several inches and fairly quickly catching one's hand. We haven't done that yet but we do observe a healthy bit of caution with the possibility.
BTW, a friend of ours relayed the idea of stuffing the front U-joint with various things that'll come out in operation. Better but...
Oh, and this friend even told us about the time he'd stuffed his front U-joint with, I think the story was, a ham sandwich!! /ubbthreads/images/graemlins/lol.gif
Tim