I was just scanning through my Scoggin-Dickey catalog and I see a brand new 350 Goodwrench long block under part # 10067353 for $1,279.99. It's built with all-new components, not rebuilt and uses a 4-bolt block as a base. It isn't a high-hp unit, but should do a pretty good job of pullin' your truck and the price is certainly right. Just add a cast iron intake with a Q-jet, HEI distributor and a set of 1 5/8" headers and you're good to go.

engine name.............350 LM1
horsepower...............249 @ 5,000
torque.......................304 @ 3,500
compression ratio......8.50:1
block..........................4-bolt, 2-piece main seal
crank..........................cast nodular
heads.........................cast iron, 72 cc chambers
valves.........................1.940" / 1.500"
cam.............................hydraulic, 0.390" / 0.410" lift
duration @ 0.050"......195 / 202

This motor should run admirably on the worst cat-piss pump gas you could find.