Greetings Cooper.
I see that you're located in WA (Australia, not US). Are you in touch with the local Cobra Club? The Perth guys/gals visited us here in Adelaide several years ago; they're a nice group.
Anyway, information from a club local to you could be beneficial regarding registration requirements. I mention that because building your own chassis to emulate the original Cobra's chassis might cause extra problems with compliance at road registration time.
If you
contact your state registration guys - they are the people who will check your car's compliance for road registration - that would be a good idea with you building your own chassis.
Best of luck, and please post updates here often
Cheers!
Glen