The stock Cobra came from the factory in the neighborhood of 235 hp. YOu added aluminum heads but they are still GT-40 design so you'll get a negligible gain. Going to the 1.7 rockers might help you a bit depending on tune. B cam will help with your 1.7's and long tubes. A 75mm MAF can never hurt and your fuel pump prolly didn't change anything. Underdrive pulleys will get you a couple. I would have estimated somewhere in the neighborhood of 265 - 270 hp. Your numbers of 258 hp and 285 tq are pretty accurate. I always tell people not to dyno their cars cause they will only end up disappointed.
I think it is pretty acurate, my understanding is thet gt-40 heads should give more tq.The hp seems ok but I would see the tq being at least in the 270's 280's