My engine is a 305 TPI. About how much horspower and torque will be added by putting in a cam with 260/260 duration .444.444 lift, and a set of Hooker Competition Shorty Headers? Im looking to build up my 305 (unfortunatly not a 350). Have any suggestions on what else to do?

 

What cam is that? I don't think it's right for your application at all.
Headers are good for ~40HP or so, with a full exhaust to match it.

 

It a computer compatible cam from comp cams. WHat makes you think it is wrong for my application?

 

If it is flat tappet, it will probably be fine.

Headers/exhaust is usually worth ~10%, and help other upgrades realize their potential. I'd say 40-60 gross flywheel HP gain would be reasonable.

 

How much of a gain can be expected by going to an aftermarket muffler? What muffler sounds closest to a factory muffler's tone?

 

the closest to factory tone muffler which also flows very well is the Dynomax super turbo I had it and it sounded just like my dads stock muffler when both running side by side.