The clutch disc should be OK - it fits the "snout" on the SM-420
The pressure plate will be OK, if it matches the clutch diameter, and if the pressure plate will bolt to flywheel (correct number/size bolts).
The flywheel is OK if it attaches to the 270 crankshaft (correct number/size bolts).
It is my understanding that the number of flywheel-to-crank shaft bolts might be different for some GMC engines/years compared to Chevrolet crankshafts.
Someone will post a correction/clarification?
(nice looking engine)
