Parts book list 2 types of jacks 8.820 #1396635 and #1377517, but it also lists 3 different bases? 8.820#1372501,#1372494,31368985. I have seen 2 styles of jacks used 1 is a T shape and the other is a stamped square . There were 3 different suppliers to GM: auto specalties ( brown tape on jack), universal tool & stamping(red tape on jack) , and california jack co ( no tape). Which one is right for your car might be a mystery? I have a early build GS and my car has the square jack in it! is right yes! is it the one that came with my car? Been trying to figure that out for years? Hope this helps! Jon