Stock GT brakes?
 

So I'm putting my SLP line locs in and i'm bleeding my brakes and I notice my front calipers say PBR on them, I check the back and they are stamped with the same thing....Are these stock GT brakes?

Size of the caliper
http://i42.photobucket.com/albums/e3...145/brake2.jpg

Showing PBR stamped
http://i42.photobucket.com/albums/e3...145/brake1.jpg

Yes, mine say the same.

ditto... noticed that when chaning to my summer shoes

yep those are stock, make sure when you bleed the brakes do all four, and make sure you have zero leaks!!!

Yeah, you just figured that out... There are only a few companies that actually manufacture braking systems. PBR is a biggie and a major OEM'er. The twin piston PBR's came on 99-04 mustang V6 and GT models. Those were an upgrade over the previous single piston that saw duty on pretty much every 79-98 in one spec or another.

Your rear calipers are PBR too IIRC. They're identical to the cobra rear caliper but mount to different brakets to fit the smaller rotor. Cobra rear rotors are vented while GT/V6 rear rotors are solid.

FWIW, GT/V6 brakes are horribly unsuitable for such a heavy car with so peppy a motor. The very first thing you should do to them is replace them with a cobra kit. Best 400 bucks you'll ever spend.