273, the good points

Wow folks, thanks for all your input. Lots of interesting things to think about.

I've seen the silverfish website, there car is pretty close to what I'd be able to do. In the UK the regs are pretty strict but the good thing is the FIA papers which I have a copy of are such bad quality you can't see the detail in the photos. I could get away with fitting an 8 3/4 for instance.
Other interesting facts, the Barracuda has to use 14in wheels but has a 4-barrel & headers. The Valiant has to use factory iron headers & a 2 barrel carb. The Barracuda has a choice of 3 different ratio gear sets where as the Valiant is just 1.
The Barracuda GT was a different set of FIA papers & I believe the 318 used for that car was the old Poly, unfortunately the GT's FIA papers were not officially issued until Feb 66 so I can't use them.
It's a real shame the FIA papers are printed on that type of paper that won't scan otherwise I'd have put them up for all to see.

I really look forward to getting stuck into this a bit more, all your enthusiasm has helped.