You may have 2 problems. Not sure if 273's did but 318's/ newer engines do which is:
1: As mentioned, hole from auto car may not be deep enough. Jig up bell on engine, measure carefully from face of bell to bottom of hole, then measure length of gearbox shaft to bell face and make sure it will clear
2: Some auto cranks are not fully finished bored for diameter. You used to get an undersized bushing to fit an "auto" crankshaft