The welch plug numbers became useless starting in the late 80's to early 90's depending on the model. Or if it was a factory replacement powerhead it came with it's own serial number on the welch plug. A dealer MIGHT be able to help you with the welch plug number, but I wish you luck. The good part is there are not that many different parts for the different years for the 1.6L cross-flow engine from about 88 on. There were some basic carb differences in the jetting, and some ignition changes, other than that the basic engine was the same since the 70's.