1666 and older had the alternator bracket bolt on the thermostat boss, 67 and newer it was off of there towards the alternator. Cakes different alternator bracket with no hole in the center. The newer Mopar performance aluminum water pump housings have both bolt bosses on them.

Another quick tell is the two water neck bolts go all the way through the ears on 1966 and older housing, on 1967 and newer the holes bottom out in the casting, they do not go through to daylight.