Vin number may be incorrect

You can get an idea of the time of year it was manufactured from the date codes on the body panels as I'm told they were generally stamped maybe as long as a month prior to assembly. For example mine has a 2 22 2D on the radiator support. Which translates to Feb 22nd, 2nd shift at Dearborn.

There were 2 different heater blower motors used in the first two years of Mustang production. A two wire single speed motor that has a dash switch with 4 positions which are off,low,med,high and a 3 wire motor with two seperate windings which make it a two speed motor built in to it which have a dash switch with 3 positions low.off,high. This information should help you determine which motor that you have and the 3 speed switch/single speed motor type have a 3 resistor bank built in to the heater case facing towards the glove box.

The two wire motor is the easier one to get and that was the later type. The 2 speed/3 wire motor came from the original Falcon models.