Hello GTA Racing - or should that read Grahame?
Ray Christopher of GTD Racing may well be able to supply a roll cage for the cabin but it takes a bit of shoe-horning in and the dash requires cutting at the edges.
Also, it's worth speaking to Malcolm MacAdam as he holds the plans for the only MSA officially approved (that I am aware of) roll bars that fit in the rear engine bay. These can be manufactured fairly easily and should pass inspection providing they are made and installed as per the details/instructions that Malc can supply. He usually provides details at no charge to club members providing that units are not then sold for commercial gain but to be sure, call him as he paid for the initial type approval.
Hope this helps and Happy New Year to all forum readers / members.