1977 GMC Pick-up Truck Differential Spool K25 - 4WD - GM 10.5 in. - 14 Bolt Cover - For Use w/30 Spline Axles - 4.10 Ratio And Down - Rear guaranteed to replace your current 1977 GMC Pick-up Truck Differential Spool K25 - 4WD - GM 10.5 in. - 14 Bolt Cover - For Use w/30 Spline Axles - 4.10 Ratio And Down - Rear. 1977 GMC Pick-up Truck Differential Spool comes new OEM 1977 GMC Pick-up Truck Differential Spool aftermarket new 1977 GMC Pick-up Truck Differential Spool of remanufactured 1977 GMC Pick-up Truck Differential Spool K25 - 4WD - GM 10.5 in. - 14 Bolt Cover - For Use w/30 Spline Axles - 4.10 Ratio And Down - Rear.