Jim--

If you haven't got one, get a Crutchfield catalogue from 800-955-3000 (web
site www.crutchfield.com) It'll give you a good idea of what speaker sizes are
available even if you don't necessarily buy from them. (although I have
boutght from them and been pleased) I have a feeling some of the 3 1/2
speakers will drop into the VW screw-off speaker mounts after clipping off a
couple of metal tabs on the speakers. Now, how you secure the 3 1/2 inch
speaker to the original speaker grill I don't know (the originals are glued?I
believe).

I just sent to Crutchfiled for some four 4" Blaupunkts on sale for $49 a pair.
They will fit in the stock opening in the door panel, but not in the stock
screw-ball mounting grill set up. I'm guessing there may be a clearance
problem between the new grills  and the window crank and the new grills and
the dashboard. In my bus the dashboard hangs a little over the speaker grill
when the door is closed.

There are window crank spacers available from www.autotech.com for the Rabbit
and Golf which should also work on a Vanangon (part # 99.837.9.135 at $20)
that will allow the cranks to clear speakers that are not flush. In fact if
your only problem with your 6.5 inch speakers is crank clearance than these
might solve your problem.

Good Luck
Jeff
83.5 Westy
NYC