8 3/4 Trac-loc?

you have a power lock ,, an excellent unit to use --- get yourself a new clutch kit make sure you have it installed correctly as the clutches have to be stacked properly for the unit to work right and the proper side bearings and have it installed into your 489 case --- the blue marks at the cross shaft ramps is case hardening from the factory to lessen wear from the cross shafts as they move up to lock up the assembly.