To be fair it is a space frame, hes just panelled the floor out in steel sheet rather than put an extra couple of small stringers in on the floor.
I do think you need to be forgetting that its a "ford". Its not. In registration terms its a custom built car designed by AG motorsport. It shouldnt matter one iota that it uses focus body panels.
You wouldnt expect someone to claim that a ferrari bodied MR2 was a ferrari and be treated as such in a race series so why should someone consider his car a OEM ford?