Thanks Bill,
I thought about the "stock on hand" thing. I also had read that the 261 was generally for the larger trucks.
The original owner opted for a front brush guard and heavy-duty rear bumper... maybe he opted for a slightly larger work-engine but not a V8? He got the standard cab so I'm thinking he really wanted a work truck.
Either way, I'm keeping my fingers crossed that this engine is rebuildable with many good parts. I have yet to remove the head, manifolds and oil pan... hopefully that will happen this evening!
I have, and already busted down, a '58 235, but the 261 is my choice for the rebuild. I'm considering this a pleasant surprise... I had thought both engines were 235's.