Thanks to Fastforward's informative Vanagon halogen light wiring
conversion info sheet, I see that the electrical socket for the European
H4 bulbs is different from the North American 9004 bulbs.  If I wanted
to avoid cutting the existing sockets in my van and soldering in H4
sockets, can I simply install the 9004 bulbs into the square E-code
fixture, or are the mechanical attachment dimensions different?  I
realize the H4 bulbs may be superior than the 9004 bulbs, but it sure
would be a pain to not be able to purchase a replacement at any FLAPS
should the need arise because they don't stock H4 and also be prevented
from using 9004's.

Thanks,
Michael