I've seen images from seom .DE sites that show a front fiberglass section very similiar to what you have drawn.
and I have wanted to 'modify' my exhisting westy style front luggage rack by cutting the middle out and bringing the front to the shortened back section, keep in mind that none of the roof contours for the front edge would match. but in general fiberglass is fairly easy to work with in custome shaping. 

and I can't seem to locate an internet reference to the pics i've seen..

though if anyone has ANY information as to this top, please share with me.  I'll be looking to accomplish something very similiar to this by using an older westy poptop section.
on my 81 diesel passenger to camper conversion
http://www.homenet.se/clindh/album/vw/aze93.jpg 

Date:    Thu, 11 Dec 2003 14:58:47 -0800
From:    "J. Harvey" <jtharvey2@HOTMAIL.COM>
Subject: Westy w/Front Sunroof (picture)

I'm looking for a picture of a Westfalia with a custom fiberglass luggage
rack that accomidates a front sunroof.  I think the van was white with round
headlights.

I drew up a quick model on the computer for fun:
http://oregonstate.edu/~harveyjo/westy_sunroof.JPG

I'd also like to see any other ideas out there.  -John

'85 Silver Sunroof
'91 GTi 2.0 8v
'76 BMW 2002