What engine do you have? I would first insure the distributor matches the engine, you appear to have the numbers for the distributor, so check against the block. There are sites online that can tell you this. Has the engine been rebuilt? Has there been a cam change? If the rotor hits the contacts inside the cap, you have the wrong rotor or cap. There is a tall cap and a short cap. Has the distributor been rebuilt?, is it it possible you have the wrong shaft? Is NAPA using the year and model of the truck or the engine to look up the parts? If your distributor matches the block and cam, you have the wrong cap and rotor.
