The Jim Carter listing listed worked exactly as described. Short shaft pump plus flat back "216 style" fan. No spacer. No belt incompatibility. Clears radiator. No muss, no fuss. 1962 engine in 1951 truck. Easy peasy.

The only remaining questions/issues I see:
* Sub-optimal fan placement for cooling. No issues for thus far for me.
* The whole car/truck balancer difference. Is that why the OP had fan clearance issues!

1951 3100