I installed a cheap (like $85) JCWhitney sunroof in my 81 Vgon, placing
it just behind the front seats, over the feet of a passenger in the
middle seat, and have been happy with it.  I drilled only one pilot hole,
and cut according to the template provided, after taping the template
carefully to the roof.  To get the headliner out of the way, I cut a 
smaller hole in it, safely within the borders of the sunroof.  Yes, em-
phatically, you do want to leave lots of extra headliner to tuck into the
frame of whatever you use, and trim after you know how much you need to
make a neat job.  I cut one corner a little too hastily, and ended with
about a .5x.5 triangle of goof visible.  The fact that a headliner
support wire went through where I wanted my sunroof complicated my job.

With the headliner pulled down out of harms way, the sabre saw did a clean
job on the sheetmetal.  I can't remember if the saw cut the yellow fiberglas
insulation pad, or if I had to do that separately with a box cutter.
Make a well-sealed basket of newspaper to catch the chips from the saw,
and CAREFULLY vacuum them off the roof and out of the rain gutter when you
are done.  On a previous car, I was casual about this step, and ended up with
several tiny little rusty metal chips embedded in my paint.  They are
incredibly sharp and will dig into the paint immediately if you put any
pressure at all on them.  Then they rust there.  Happily, that practice run
was a Plymouth Voyager, so no loss.

Sunroof is a good idea on a no-Air-Co Vgon; quieter when open than any
window, and safer open in a parking lot.  Also you can stand up through
it to wax the roof, which is not possible with a roof vent except in the
last stages of anorexia.

Good luck!
B.
Wm Kennedy
kennedy@admin.njit.edu