A 305 is not the best sbc to make loads of power. You can be thankful for 8 cylinders offering powerstrokes per rpm, and a 3.48 stroke to pull. Vortec heads , summit headers, a performer cam and intake with 3.73 gears , made a big difference from stock.
A cam is good , but if you are not sinking a ton into it, stay mild. Vortec 350 1.94int heads work good/cheap in a 305, just mill them to cc. The newer ls6 beehive spring and small retainer is a stable valvetrain for a performer cam.
A low profile supercharger will get you rethinking the 305 potential. Mucho bueno.