New car, now I need some info.

[OneQuick6]

Ok guys. I just bought a 97 Ford Mustang Cobra. It has 18" Cobra R rims.
I bought the car at a dealer, and got in touch with the previous owner. He said, that with a 4:10 gear, H-pipe, cat-back, and a cam for the motor, he ran a 12.7 . Is this possible? Also, the car no longer has the
H-Pipe, that I'm sure of, but the cat-back is from mac and sounds good. I don't know if it still has the 4:10 or cam or not. I don't really have the experience to take the motor apart to find out. So could someone give me stock 1/4 e.t's . And stock dyno numbers. Also, how much should I expect to pay $$$ to get the car on a rwd dyno? Also, I'd like to get a custom H-pipe or X ( crossover ) pipe, what would be better for sound+performance. How much can I expect to gain from that simple mod. I don't want an 11 second street car, if I can run a 13.0 on the street, I'll be happy, I'd guess that would translate into a 12.7 ( approx ) at the track.
For the cobra, how do these mods sound? An H or X pipe, and a ramair setup. That will be all I do if the car already has 4:10's then I am done, if not I'll add a gear setup 3.7.3 or 4:10 not sure. How much power can I expect from an Hpipe and Ramair setup? How much can I expect to pay for ramair $250??? and about $50 for the H-pipe, I can pretty much make it myself at cost. Is 3" the optimal diameter? smaller or bigger?
As far as the gears, I've noticed that 2nd gear runs out in the 50mph range, does that sound like a 4:10??? Thanks for everyones input, it is greatly appreciated for those of you who help me. Thanks.