I just went through all this misery with a Gp2 RS1600 build for an FIA HTP. The HTP general regs require the Mk1 Escort rollcage only touch the bodyshell at 6 points and the rear legs have to be mounted to the inner wheel arches (cannot touch the shock turrets like a Mk2 if turrets are fitted). What is more confusing is that the HRCR HVIF allows 14 points of contact so my cage is a Custom cages job with bolt/tab contacts in 8 additional places that can be removed for FIA events.
http://www.customcages.co.uk/Rollcag...&type=Historic