Well, I'll throw in my two cents as well--
It's a GREAT looking truck. I don't think a guy could ask for a better starting point. The short-bed 1/2 tons are the more popular...I'd think in the mid-west (Michigan, Ohio, Wisconsin), your truck would sell easily for $5,000.
I've started a business too, though it's on the side and a lot less high-pressure. I have a regular day-job, so at this point I'm not scrimping. What's your business? Is it one that an old truck could be a part of? Like, putting your name on the door of the truck?
Now, about the fuel exonomy thing: You could pick up some mph by putting a manual 4spd overdrive trans from a later Chevy pick-up in it. It'll require a trans cross member, but that's pretty easy--there might even be a bolt-in one available out there already. I've got that trans and bellhousing from an '87 Chevy, so do a search and find out what other years will interchange with that transmission.
You could also go to a more fuel-friendly gear in the rear end. It probably has some pretty steep gears in it now...drop down to something in the 3.40 range. It'll kill towing power and grunt, but will get better mileage.
Ditch the 4bbl in place of a 2bbl carb--that'll help by keeping your foot out of the 4bbl.
A good free-flowing dual exhaust will help too.
This isn't going to make the truck pick up 15mpg over what you have now, but it'll help.
Otherwise, like was said earlier...pick up a cheap econo-box.
-Brad
