VIN engine code M = 1974/76 F100/350 390 4V.

1974/76 were the only years that Ford offered a 4V on a 390 installed in an F100/350.

1968/76 F100/350 390 2V: The VIN engine code is an H.

The heads used on 1974/76 390's are not the same as 1968/70 390/428 heads with a casting number of C8AE-H.

1974/76 390 2V/4V head casting number prefixes could be D4TE, D5TE or D6TE...some of which depends on whether a smog pump is present...or not.