A friend bought a 73 GMC 2 years ago. He and his wife just love it. He call me last Spring to tell me that it wouldn't start. I went over to find the problem. The distributor points needed to be replaced. Put new points in. And they were back on the road. I told him that it might be a good idea to call Dick Paterson for one of his HEI distributor. ( The GM HEI distributor is an outstanding unit. ) About 2 weeks ago he calls to tell me that he took my advice and went to a salvage yard to get a HEI distributor out of some Olds engine last Aug. He said that the HEI distributor was great. But there seemed to be some other problem. As the 455 just didn't seem to climb hills like it use too. (This info is more for the newer guys on this site. As it's been discussed before. ) Our CMC engines are different then the car engine. The differences are small. But make a real difference in performance, and operation. The GMC engine operates in a lower RPM range then the car due to the larger size of the tires. Thus less revs per mile. The GMC has alot more mass to deal with. The GMC engine differences are the distributor, carb, and cam on the performance side. And the water pump, and intake manifold. But that's another topic. ( the trans is stronger then the car trans. But that too is another topic. ) For the motor home engine to perform well under these operating conditions. The distributor advance curve needed to be altered to conform to the altered camshaft. And the carb had changes to perform correctly with the distributor, and camshaft. That's the short version of the story. So if you want to put a car engine in your GMC. These changes need to be made. So never trash these important components. Dick Paterson has these items. And is vary knowledgeable in this area.