I've read up on this some, but there is still some mystery here to me. Not being a GM guy at all, I'm looking for some advice here. Previous owner installed a 350/350 into my truck. The 350 trans is leaking like crazy, but seems to shift fine and be OK otherwise. It will need to be pulled to fix the leak, so I'm wondering if there is a better choice to put in there now and just replace it (TH400 / 700R4 etc)? OD would be nice, but not critical. Either seem to be cheap and plentiful in the area. I would rather not mess with the driveshaft at this point, but I don't know if the lenghts change or not. Thanks!