John
Guest
The Series 3 started with Serial n changes in 82, looks like Sn4501 for the N5 and this comes from the service manual. Also the Series 3 has the American Bosch fuel injection system, the earlier have Roosamaster pump and AC Nozzles. Also the Engine Block catalog n for the Series 3 is 4036830, the earlier models are block n4036512. These are the easiest way to tell. The Series 3 in all 3 models 5,6,7 were built heavier, but you have to about see them side by side to tell the difference, I have a local salvage yard that has both earlier and Series 3 and newer N's and when there, the difference can be seen. QUICKEST check is the AmBac fuel system, open the steps to the engine compartment and look at the pump, Ambac is a Series 3 or newer. If I can be of any more help, just ask. John