http://67-72chevytrucks.com/vboard/s...d.php?t=590959
2nd page post 26, lists a chart for 72., your code:
Prefix: RJJ, Model: KE20, ratio: 4:10N,
*N designation is No Spin.
There is still a good possibility this is an HO52 not a 72, some Ho52's utilized the same ring gear and load bolt, the brakes were however larger.