Don't want to start a pissing contest, but Ford did not have any crate engine program till the late 80's, Up until then we would pull the motors from the assembly (read: not engine plants). So motors were as they would have been on production cars. IIRC motors in the parts system were long block & short blocks, NO drop-in or dressed assemblies. So in theory yes 289 may have been available, but highly improbable as the cost and labour would have been much higher (DeT was a cheapskate) Mark and Jerry have supplied engine tags and the motors are J code motors.
FWIW: I have spent a few hour doing the research and will stand by my findings.
John: the repro Autolite plug wires look right but are not very good, most early mustang restorers use Taylor brand wires, they need to be custom fitted but look right and last a long time.
deniscCaretaker of 8MA1244 '70 Euro Mangusta DRIVE THEM, THEY WERE MEANT TO BE DRIVEN, IF YOU WANT TO LOOK AT ONE, BUY A POSTER!