If you have the ID plate, then printed on the plate to the left should be the letters "TO" or "TE". Based on the number it is not a TO-30. TO-30 s/n STARTED AT 60,000. Both the TE-20 and the TO-20 could have a SN in the 47,953 range. TE's ended with 48,000.
Since your casting start with TO then you have a 1951- TO-20 Manufactured by Harry Ferguson Inc. in Detroit, Mi.