I've been doing a bit of research on this old question, since the FIA published all the old rule sets (appendix J to the International Sporting Code). Anyway, there're enough referencable material that I've been able to write it up on the Wikipedia page for the TR7 in the "motoresport" section -
https://en.wikipedia.org/wiki/Triumph_TR7#Motorsports.
The only bit that's still not clear from the rules is how Bill got them to approve the hd rear axle before they made enough (1000) 5-speed cars. It's listed in the papers as an export option, but there's nothing I can find in appendix J that covers axles that way for group 3.
Still, the issues about the 16-valve head, close-ratio box, and overdrive under the 100-off rule, and the brakes, etc., under (what I suppose, by analogy, must be called) the "0-off rule" are now clarified. Up until the end of 1977, that is. Then the issue over the head gets really, really interesting. Nearly as interesting as Vauxhall's problem with the Lotus 16-valve head and the scrutineers at Rally Portugal in 1978.
