Your 305 is perfectly capable of getting 300hp. The whole 350 4 bolt main is a joke. A 350 is a nice engine solely because it was available in almost everything, and has multiple speed parts available for it.
Facts: your 305 has the exact same crank that a 350 has.
any part that bolts onto a 350 of the same year, will bolt onto your 305, minus the pistons.
heat is your major enemy in a 305, as the factory heads are pron to cracking at the slightest over heating.
Now, you say it feels doggy, the first thing to do, is get it back into factory working order. Plugs, Wires, Distributor cap, rotary button, vacuum lines, oil change, fuel filter, air cleaner, transmission filter change, clean out fuel return lines, and fix any vacuum leaks that it may have. Clean all wire connections. Then its time to get a baseline feel of what your working with.
As far as bolt on parts, Start with a nice set of After market headers, and dual exhaust with a crossover pipe. This will be the biggest bang for the buck, and every other part you add after will gain its full potential.
Second I would switch the rocker arms from the factory 1.5:1 ratio, to a set of roller rockers with a 1.6:1 ratio. Remember these rockers will be usable on replacement heads later, as well as on the heads of a 350 should you choose to upgrade the block later.
If your car has over 50,000 miles on the odometer I would strongly consider replacing the Timing chain and gears, prevention is the key here.
After those changes hp is achieved the same across any engine, increase airflow, and then provide the correct amount of fuel to that amount of air. But the tune up, exhaust, and rocker arms should get you around 45 horses by themselves. Which you will definately feel in the seat of your pants.
Another alternative, is to change the gear ratio in your rearend. Going from the stock 3.07:1 gears to a set of 3.42:1 or even 3.73:1 will definately wake up the acceleration of your car, though you will lose some top end in doing so.