Thanks for your help - I now have the AC Cobras & Shelby GT350 using the mustang sounds. Yesterday I found new sounds in the downloads section for the AC Cobra, and another one for the Shelby, which I will install later.
I also found the other missing car that I had forgotten about. It is the Porsche 914. I cant find sounds for it, so I am using the Porsche 911 sounds on it (It's better than silence).
For some reason all these sound files dissapeared, I have no idea why, unless it was when I tried to install the 'bude car class patch manually before I found out that you use their updater for it.