I wouldnt say thats ridiculously fast. 96-98 Cobras normaly run mid 13s on street tires at sea level. Just a good set of slicks and skinnies can put those cars in the 13.00 range. With bolt-ons and gears, i would expect the car to run mid 12s. On street tires? I dont know that seems fishy.... but 12.50s isnt un-common for a bolt-on SN95 Cobra with a good set of tires.The 96-98 Cobra have the solid axle and it is 28 spline.
Also, are you really running that time? If that time translates like the post above says, 12.50 for a N/A SN95 Cobra is ridiculously fast. Hell, if it had slicks I'd say that is too fast. Hell, you're spinning too?
Don't dump the clutch on your daily driver. Slip it quickly, not worth that minor time improvement. I'd rather burn my clutch up than replace transmissions and rear ends.