Google turns this up: http://67-72chevytrucks.com/vboard/showthread.php?t=177141

If that looks like yours, you have an Eaton rear. Not sure how to decode the numbers, but the Eaton HO52/HO72 was used from 1947 to 1972.


Some of my crap:
1963 C-30 flatbed dually 292/SM420
1965 C-10 LWB fleet 250/column shift 3 speed
1965 C-30 9' stepside 250/SM420/4.10 gears (my DD)

Website I made for my crap:
http://www.66submarine.com