My original concern was weather or not the Mr Gasket t-stat would fit, since all the online parts businesses (NAPA, AutoZone, O'Reilly's, etc) did not go back to 1965.
Some additional information for 66 and older Mustangs, for unknown reasons most car parts stores' computers cover 1967 and newer, so if you need something for a 65 or 66 engine ask for a 67 non smog. This applies to I-6 and V-8 engines. There are exceptions, like the water pump on 65 V-8 engines is aluminum, but plugs, points, filters (all oil, most fuel), thermostats, etc, are the same.
Jim