I am both elated and terrified to report that the SN95 Cobra springs DO, in fact, fit.
HOWEVER!!!!!! Its not a pleasant sight.
I'd like to confirm the speculation and previous research performed by those that have come before. (Click here for reference.
-The rear springs have similar dimensions to the stock MN12 springs.
The rears are a direct bolt in replacement, though as mentioned, thunderbirds use a progressive rate spring and the Cobra does not.
-The fronts won't even be close. They're shorter, wider and even if they did fit their spring rate will be far too high for MN12's coilover placement.
While they do "bolt in" to the struts, and still fit into the spring isolators, albeit are slightly smaller in outer diameter, they are considerably shorter than the stock MN12 springs. In fact, when using the wall mounted spring compressor at work to swap them, hardly any compression was needed to install the top hat nut.
While I do not have pictures currently, (i forgot my phone at home today :/ ) I can safely say the front of the car is easily 4 inches lower than stock and the rear is either stock height or slightly higher. As reference, the front fender is about half inch higher than the tire tread. With this information, I don't believe it unreasonable to use Cobra fronts and an adjustable rear coilover setup designed for a Cobra (since the shocks are bolt in) to even the height, though custom spring rates may be advised. Heck, as is, this could be a cheap suspension alternative for someone trying to get into drag racing.
I will make sure to take pictures when I head into work tomorrow, but it looks silly without fancy wheels and tires...which may be the next step for this bird, not sure...