Rick,,,
First of all WELCOME to the addiction !!! Hope to see you in October,,, Man I love 70 Bird's..
Now to help with a few of your questions.
To run at Maxton you need to be a member of ECTA ($50 per year) but since this is late in the year, I think it will only cost you $25.. that gets you a car # and yes even for T/O you have to be a member with a car # also you have to register for the event.. $100 pre register ($120 at the event , I think).,
Tires, Yes S OR T rated would be OK for your speed,, however with 12 year old cracked tires, they would probably flunk tech,,, personally, I would get a new set of tires,, and if buying a new set for a 1970 Firebird, I would get a new set of BF GoodRich T/A Radials .. they are close to period correct for your car, have many sizes and are H Rated,, which allows you to run up to 150mph,, should be under $400 for a set mounted, balanced out the door.
If you have a more modern lowered look on the car and want low profile tires you can get Fuzion ZRI
tires and are Z rated hook good and cost about the same,,,
Hope this helps.
Charles