A half cage can be. I couldn't get the front hoops in a ANDRA spec cage mod plates on my Silvia. I'm pretty sure side bars along the door canbe plated though. Someone here will no the law more then me as it's been years since I've had one done. Also, your not allowed to carry people in the back with a cage, so the trim will have to go. As ur running a 2 seater this wouldnt matter anyway.
Seats, you need to weld up the seat belt holes, so belts cant be replaced later on. I have yet to met someone who will over look this, agian - Someone might. it's been years since I have had it done.