My favorite car I ever owned was a 1972 Mercury Montego, which had a 351 Cleveland High Output block in it. Was a semi-hemi. Ready for the punch line? It had an automatic transmission. Never figured out why, but I could lay rubber in passing gear. LOL.
Auto trans in a Montego? Not all that surprising. The Montego was the Mercury version of Starsky and Hutch...basically a Gran Torino Sport package with a Mercury badge.
I'm pretty sure that it was the Lima based 3-8-5 engine series that were the semi-hemis...think Boss 429.
But the 351 Cleveland definitely was a mighty contender, no doubt about it. I'm betting you had a 4:11 diff in that rig, or maybe a 3.73.