Nomex / Safety ?'s

[Kputz]

Do yourself a favor Roger and have someone reputable and experienced build a cage for you, and insist on the nascar door bars and a shin kicker bar (post to post under the dash). Miata's have limited room inside and most bolt in cages or bolt/weld in cages are designed for any number of cars. You'll want as much room as is possible in the Miata and the cage builder and find you an inch here or there. The costs will be close, but the custom job will usually be a bit higher. To accomplish this you'll have to remove to cut the dash which means you should just bite the bullit and trash the car and make it a dedicated racer, removing everything allowable under the rules. This gets out of the car most of the stuff that can burn, which is important in case of fire. Remember too that most fire victims are not burn victims, but rather choke to death on toxic smoke from burning material (read nylon, phony leather vinyl, etc.), stuff that a fire system will put out but which will continue to smoulder. With or without your lung situation that's probably not wise.
Check out www.specmiata.com and use their search engine for rules, hints, suggestions, and answers to most newbie questions.