I replaced my non-standard antenna with one from
the Bus Depot and it could be installed totally
from "outside the hole" with no need to remove the
headlights or anything.  I could fish the cable
from under the dash to the radio; maybe I removed
the instrument panel cover, I don't remember....
Anyway, the hole in the body (original) was right.
It was a slight puzzle to figure out how to install
it from the outside, but certainly easier than
doing your taxes.  ;-)

I think it was this one:
http://www.vanagain.com/images/251035503r.jpg
Maybe the same as this:
http://busdepot.com/busdepot/details.jsp?partnumber=FM09VH
It totally retracts and uses a small "key" to grab the
tip to pull it out again.  I'm pretty sure I paid the
$14.95 rather than the $45.00.  I don't remember where
it was made, but the quality seemed just fine.

                                Richard A Jones
                                Boulder, Colorado