That block casting looks a lot like the later (1965 and later)H.D. truck 413 blocks shock
I built a 1972 413 Truck H.D. block for my 1963 Fury street car, I'm going to pull the oil pan off and take a look inside to see if it has those bosses luck

Mr.Cab Racing and winning with Mopars since 1964. (Old F--t, Huh)