Disclaimer:  I have never installed an automatic trans into a Vanagon, only
taken one out.  Having said that, the following information most likely
holds true.

PSA for installing automatic trans:

Most torque converters have to be properly seated to engage the oil pump
drive.
If the converter is not fully seated and you try to install the trans to the
motor and crank down on the bellhousing bolts you will most likely trash the
pump.
With the transmission assembled and torque converter hanging on the input
shaft, push in on the torque converter while turning it by hand.  You should
get to a point where the converter moves inward an inch or more and makes an
audible clunk.  Now you are safe to install the trans to motor.

I had a good friend change his trans in his Ford F150 and didn't seat the
converter.  Guess what?  Fail.

My personal experience includes a Mercedes 240D, Geo metro, VW Jetta,
Pontiac Firebird V6, and others I can't remember.  All required the
converter to be seated.

Hopefully this will help someone some day.