I can't answer those specific questions (the bolded part) for your car in its current condition.I always wanted the BFGs, but for my truck (i run 33x12.5 on 20s) it would be a fortune. Good to know the letters turn brown, maybe i will stay away for sure now. I was looking at Cooper Cobras. Tires are a long way down the road though. The more i look at this nova the more problems i find. Might be out of my league on this one!
Anyway, after doing some looking, my rears are 225/70/14 and the fronts are 195/75/14. Lets say i stay that size or go up/down, my question is: are the rims specific to the axel? Like can i put the rear rim on the front? Any weird backspacing i should know about? If i pull the rims, sandblast them, paint them, do i need to worry about front or back since there is no tire on them?
When it left the factory, it had 4 identical wheels with 4 identical E78-14 tires installed on it. With this kind of "find," it's best to check all 4 tires. I've seen cars in this condition where every tire was unique (different manufacturer/model tire, and different sizes). I've seen lots of cars on the road with 3 different sizes on them (ones that drove in to my shop that way). I've also seen cars with 3 or 4 different wheel designs installed (different backspacing/offset, different widths).
You seem to be very aware of what to look for. The only way to know what you have on your car is to take the wheels off, lay a straight edge across the back of the rim and measure the backspacing. When you get the junk tires dismounted, you can measure the width of the rims as well. If your rear wheels are wider than the front wheels, you may want to stay with a "staggered" setup, with 70 series tires on the rear and 75 series on the front, or go to 70 series on the front and 60 series on the rear. If all 4 wheels are the same width and the same backspacing, I'd recommend going with identical tires on all 4 corners. "Staggered" setups with identical wheels look goofy IMO, and they can have weird handling issues sometimes.
Your speedometer is calibrated for ~790 revolutions per mile on the driven wheel, or about a 25.5" outer diameter tire. If you deviate from that, your speedometer will be off. Smaller outer diameter/more revs per mile is generally a better choice than larger. With larger tires, when "officer Friendly" asks if you know how fast you were going, your actual speed on his radar gun will be higher than the number on your speedometer. With smaller tires, the number on the radar gun will be lower than what you see on your speedometer. Everyone thinks "I'll know that, and drive accordingly." I used to think that, too. Until I forgot one day driving a vehicle I had oversized tires on, and I got caught going faster than I realized.