Dave
I have one of two cars fitted with Pets's full roll cage. The other is with John_Tiemann in USA. He has posted here in the past.
http://www.gt40s.com/ubbthreads/dosearch...&fromprof=1
My understanding is that the cage itself cannot be certified by CAMS, until the car is finished, then the cage is certified as part of the complete car.
I wanted CAMS certification for mine, but Pete has been able to supply a detailed installation booklet showing the design of the cage, copies of the certifications for the steel used etc, etc, which would be used in evidence when CAMS came to certify the car.
As I understand it, if Pete is building you a turnkey he should be able to get the certification after the car is finished, around the same time as rego.
It is not too difficult to get into as far as I can tell at the moment.
All the best
Lee