what would a set of after market heads and cams, with long tubes high flow h pipe and cat backs do for power increase to the wheel on one of them bad *** 03 -04 cobras?

 

not as much as a twin screw... go twin screw instead of the money you'll dump into heads, cams and longtubes... the gains aren't worth it compared to a new blower.

Honestly, I wouldn't be able to tell you for sure how much of a gain you'll see... cams probably 15-25rwhp, same for LT's, and heads not sure to be honest... With a stock motor, and a 2.6/2.8KB you will see over 600rwhp, in some cases over 650rwhp (depending on your bolt ons), with the BAP, MAF, Cooling mods and tune.

 

+1 above, the money spent is much more worth it with the twin screw and will make much more power with a kb or whipple...
Also, you dont need to change the heads and or cams because unless your gonna push over 800hp dont worry about it and thats my 2cents