[GMC Jim]

Checking the advance curves for the various years of Chev/GMC engines; find that the centrifigal advance falls into the range of 8 to 12 @ 200O RPM. for 6 cylinder engines 1971 thru 1980. So; it would appear most any HEI unit within that range would perform satisfactorly. However, the mechanical condition should be checked; end play, etc.......Note that there is considerable difference in advance curves for the variious years and models of V-8 engines....Installing an HEI distributor with a radically different advance curve than the original distributor will result in decreased performance....best to take used HEI unit to a qualified distributor rebuild shop. They have the distibutor machines; weights and springs to match the HEI unit to the specs required for the engine it will be installed in.