First you will need to find the buck tag located on the radiator support on Dearborn Cars it's on the driverside upper on San Jose cars it's on the lower. The 76 Was built by motortown and not ford. The big differences were the Door Panels the 76 Should have brushed aluminum door panles with a rectangular block that has COBRAII in it but door panels can be swapped if the Buck tag is there look for the code CB. You may want to try
www.mustangii.org and sign up for the mailing list. Those guys can be a little abrasive but should be able to answer most questions.