I've seen those 505 numbers cast into the right side of the case. They are Detroit Gear casting numbers and possibly a date code, but I don't know how to read them. Look at the serial number plate riveted to the left side of the main case. Read the model number, serial number, and tell us what color the plate is if there is any paint left on it.
Studebaker helped develop this transmission, and used it from 1950 through 1955 and on a few '56 cars. It was used in Stude pickups for a couple years, and also in various other US and European cars and trucks.