Lots of the 460 truck motors had external oil coolers. They're actually pretty nice units, with AN fittings and all.
X2 on dano's advice to go to a carb setup. I stuck with EFI on my 521 stroker build, and the heads/intake were definitely the bottleneck in the engine's breathing (not to mention the frustration and cost of tuning it).
Nice truck by the way. It makes me miss my '70 F100.
Scott