HP Estimates??

Hi guys I have a setup in mind but I don't know what kind of power to expect. I have a 1969 Mustang Mach1 with a 351 Windsor. The car put down 155rwhp on the dyno without any mods (seems awfully low even for my elevation). I have just barely put on my exhaust system(Check Sig). What do you guys think that would have bumped me upto. Also I plan on putting AFR 185's, performer RPM(Airgap if it fits under hood with stock aircleaner), and Comp Cams Camshaft don't know which one yet. I want to keep the stock converter. I am at 5000 ft elevation in Utah. My goal is 400 fwhp. Feasible?? What will the setup put me up around?? And what do you guys think the exhaust did for me and put me at right now??

Yeah actually that is what I was exactly planning to do with my rear. To put in 3.50 posi but that will come last. So the exhaust has probably put me to 185 rwhp now?

Ahh man that's true. But my car had around 300 hp from the factory. 155 rwhp @ 3500 is just depressing even at 5000 ft elevation I think its still a little low. Maybe I am in need of a tuning. The only thing that makes it feel fast is the monstrous torque it has but then my car will crap out after 3500 rpm. Anyways more suggestions guys. I love this hobby.