......................................The suspension needs to be better located - so brackets for A-arms need to be added, shock absorber mounts repositioned and so on. Can these be cut into the unibody interior metal work? Could the cage penetrate firewalls and other interior metal and then be used for attachment points for these mounting points?......................
I can see where you are trying to go with the cage and I guess you are just going to have to get some kind of ruling on it with the chair in that class. Let us know what you find out or maybe there will be comments here. One thing is it says "The following items shall be retained in the stock location and of the same year as the body: frame, fenders......". In your case the unibody is the frame and you are leaving it in its original position, so I wonder if the cage extensions that could act as suspension supports would be legal, but don't feel so as that is not listed in the "permitted" items.
I'm sure you read the part about not changing a front wheel drive to a rear wheel drive.
Looks to me the class is to let someone run a production car with a slight modification to it like a motor change, quick change, or non-stock supercharger and where you are trying to go is more in comp coupe territory as you mentioned.
Driving back from Missouri to Utah I noticed a couple of the new mini-coopers and though they would make a pretty good basis for a comp coupe car. The front isn't aero, but you throw that part of the car away anyway.
So move up to comp coupe and go for it
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Sum