I'm a friend of Captain Mattirex, and I think I can answer part of this for him.
The reason the alloys are not standard on his version is due to the game only having one set of Vauxhall alloys as standard, which are different from the ones on the real car. Plus, you can't colour them. So he picked the alloys that were closest and used them. I'm currently making the VX Racing Vauxhalls and facing the same problem.
We run a website called the Forza 2 British Grand Touring Association. From it, we run two primary series, the British GT and the BTCC, and a few side series, for instance our GRID championship. We have been looking at starting some new championships, and one of them we plumped for was the Sport Maxx series.
Check it our here.
http://forza2britishgt.co.uk/home.htm and remember to check out the forums!