I have dropped my tranny myself several times. I have done it both ways with the engine and without. If you arenot going to drop the engine as well then make sure you support the engine. you can make a simple tranny jack from a  floor jack by simply removing the cup and replacing it with a double h made of tube steel from a local welder(about ten bucks). If you have access to a pump jack(one used to unload trucks) this is even easier as all you have to do is drop it on the forks and then pull it out. 
    My personal feeling is that it is much easier to drop engine and tranny in one piece. You can better reattach the tranny to the engine on the ground and make sure that the torque converter is fully installed and properly torqued.
    In both cases I used ramps instead of jack stands to keep the van in the air.
Best of luck
Patrick Bishop, 85 westy, Appin Ont