OK
I'm sticking with Keith's answer, because Eric Broadley was well on with creating a 40" to 41" high design before the 1962 FIA rules were finalised. However, although no specific total height was stipulated in these rules, in a roundabout way there was a minimum legal height for a GT car.
The rules stated that the minimum height from the lowest point of the seat to the roof was 85cm (33.5"). Add this to the minimum FIA ground clearance of 12cm (4.8"), add 0.5" for the thickness/curve of the roof, and say 1.7" for the seat base/floor, and you reach Allan's magic 40.5" ie the minimum height possible under FIA Appendix J rules!
OK it's probably wrong but it sounds pretty convincing to me /ubbthreads/images/graemlins/smirk.gif!
So if Keith gets a CAV, I want a real one - any colour will do /ubbthreads/images/graemlins/grin.gif.
Thanks!
Rob