I'll take first shot at this one. For a work truck, keep the six. The 283 is a solid engine, but makes most power and torque at much higher RPM's than the 292. For low-end grunt, like hauling loads and pulling trailers, the bottom end torque of a big inline six is hard to beat.
The 283 would be OK with the 3.73 (if that's what you have), since it could rev high enough under most driving conditions. But, when you head up the hill with a load, the 292 will pull away.
Someone here probably has the factory HP/Torque numbers and RPM ranges to back this up (or prove me wrong!!!).
Regardless, sounds like a good deal on the truck...better post some pics!
SSOW...
