I think that a few of these Mustangs had four bangers.
You’re absolutely right and I knew after I re-read my post that someone would rightly refute my “never”. But then we were speaking about the ‘64 1/2 - ‘65 Mustang so that part, at least, is true. And if you want to take it further the Mustang, in all configurations, has had a bunch of different engines; fours, sixes (straight and V-6) and eights including 260, 289, 302 (Windsor and Cleveland), 351 (Windsor and Cleveland), 390, 428 (Shelby), 429 (Shelby), 460 (Police) and, lest we forget our dragster brethern, 427 in several different head designs, not to mention the 427 SOHC. More recent versions have reduced CID due to making more power with electonic fuel injection and aluminum heads with 4 valves per cylinder (a highly exotic thought in my time) now commonplace.