Can you post a pic of your squirrel cage too? There have been batches even of the correct motor, where the fan/cage supplied was not the correct one and the offset made it virtually impossible to fit. But that did not effect the motor mounting itself, so you still have to deal with that unfortunately.
I don't know for a fact we still use it, but the traditional upgrade was not a Ford motor at all, but a GM motor that was larger, more powerful and had a larger fan. In recent years there have been others that have used a later model Ford motor and fan, but I don't remember what that was out of.
I'm sure there are old threads here though, that would indicate what Ford model was compatible.
If it was from a truck though, it must've been an '80 through '86 then, because your motor fits just about everything else! I don't remember it being a motor from the '70's, but I would not want to trust my memory on that score.
Sorry to hear you're having this trouble. It's hard enough cutting through the old box with the parts that do fit!
Good luck.
Paul