The Vortec head swap is a great idea, since the stock heads really suck. It will give you better flowing heads, and about one more point of compression. More folks should start out with a head swap, since its hard to get anything good out of the stock smog-era heads. You might also want to take a look at this Engine Masters episode on Youtube to get an idea of where you should be headed.
https://www.youtube.com/watch?v=f7mvgf6_p1g&t=829sDo you know the stock gear ratio in the truck? With an unmodified TH350 (stock stall converter) and 33s or 35s, you really need at least 4.10 gears. These were common on 3/4 ton trucks, but 1/2 tons often had higher gears (3.07, 3.42, etc.). Finding a donor truck with the right ratio and swapping both axles is often the simplest choice. If you are willing to swap torque converters, a higher stall converter (2500-2800 rpm, etc.) would get your RPM up faster and give you more on the low end as it kicks in.
When you compare cams, don't be confused by articles where the engine is going into a Camaro or other vehicle that is much lighter than your truck, or into a car that has a 4 speed (where you can rev it up and drop the clutch). You want more power, but don't want to kill your low end torque. With your Vortec heads, a cam in the range of 214-218 @ .050 is usually a good choice, and should make up to about 325-330 HP if you also use long tube headers, full duals, and a good carburetor. Many vendors refer to this as an RV cam. You could use more cam (e.g. 225-230 duration @.050) and get more total horsepower, but would probably lose some of the low end torque you need.
Make sure you check the total lift on any cam you buy, to ensure it will work with the Vortec heads. Scoggin-Dickey heads may have been reworked to allow for more lift, but stock Vortec heads can only handle about .450 lift before springs bind.
Bruce