I learned about it in a Mopar Muscle article:

360 Budget Rebuild: Double Take 360 Pt. 1 December 1999
360 Budget Rebuild: Double Take 360 Pt. 2
January 2000
360 Budget Rebuild: Double Take 360 Pt. 3 February 2000

Just cut a grove in the rocker shaft at a 45 degree angle centered on the oil hole. I don't remember if it gave specifics on depths or lengths.