The no trouble one-to-get is the 3 valve that has the later head and 100 k plugs, plus if you can get the 4R75 trans (don't know how they are spec'd) there is a thread stating the 75 has beefier internals.
Many people on there are complaining about the plug blow out issue. On the other hand, if someone has a solid van with the blow out issue I bet you can buy it for short money...the repair does not require head removal, it just takes some mechanical aptitude. There is a really good series of posts in there on how to deal with it. I would think the main issue with a van is accessing the plug hole. Posts in the forum seem to indicate that #3 on the right side is the most common blow out. Before the blow out people think the have a lifter noise or manifold leak but it's actually the plug hole "breathing"

Good luck