RAC comprehensively insured my car with all the mods disclosed. I faxed them a two page list including pillar mount guages, forged pistons, FMIC, custom pipe work, surge tank, etc.etc. for their record, as I didn't want any 'drama' in the event of a claim. That was 4 years ago when very few insurers would cover a rex and even fewer for a modified one. Not sure if they changed their position now.

Other car is also insured with RAC and I was happy with they way they handled my recent claim and the quality of repair. So I would recommend giving them a call.