You're specifying pulling power, not "I want 500 hp so I can boil my tires!" Good thing, that's cheaper.
From what I can tell, there are two valve sizes on the TBI heads. I believe the 305s got 1.84" intake valves and the 350s got 1.94s. I'd bet you have 1.94" valves, but if you take the heads off, verify. GM does silly stuff on a whim. If you have the 1.94s, I'd do a cleanup port on the heads. Don't touch the swirl ramps except to clean them up. Headbytes Porting on Youtube has a good video series on TBI heads, but I'll say enlarging the combustion chamber to unshroud the intake valve is pretty difficult - I skipped that part on my heads.
Call your favorite cam manufacturer and ask them for a cam. In my truck, Lunati recommended a big lift, short duration cam for me that's very impressive down low.
What does your exhaust look like? Pencil thin pipes, crushed down to half size with crinkle bends? Headers and a crossover make a nice difference.
Finally, consider tire size alongside your gearing. If you're running tall tires and don't expect to swap down in size, you'll want a higher rear ratio. If you're interested in shorter tires, gears might not be necessary. When I autocross my Mustang, I swap on tires with 2" shorter height. It puts me right in my power band at autocross speeds.