Hi Simon, sorry I haven't replied before, but I guess this posting came in when I was on holiday, and I've only just spotted it. I found a few useful links, the best one (I think) is http://www.streetfire.net/video/victory-by-design-porsche-925_170734.htm, it's a short documentary about the car commentated by Alain de Cadanet. Also Wikipedia has a page about them, with a couple of pictures, and some useful links at the bottom of the page listing chassis numbers, liveries, etc, try en.wikipedia.org/wiki/Porsche_935. The other useful one I found is http://www.racingsportscars.com/type/photo/Porsche/935.html.
Hope this helps, and looking forward to seeing the finished kit!
Regards
George