HEH-T Toploader ???

If you search the RESEARCH forum and you'll see this discussed previously

Do not be alarmed! My toploader is also an HEH-T. The car was built in Detroit on April 22, 1965. And yes, there is no VIN stamped on it nor on the engine block although the casting and assembly dates on the motor and the casting dates on the tranny parts are correct for the build date of the car. I am the third owner, have talked at length with the two previous owners and am certain neither the transmission or engine has ever been replaced. The book you are looking at is in error about the time the HEH-T was used. Also look carefully at the factory assembly manuals and you will find a footnote that indicates that stamping the VIN on the engines and transmissions was an option with the "K" engine, thus all are not stamped. My transmission ID # is 024120, and is stamped on the same tag as the HEH-T identification. Check the casting dates on the external compoments of your transmission and the casting date as well as the assembly date stamped on the driver side of the engine block, sticking out past the front of the left cylinder head. Components with no VIN stamp are more common than most imagine. I beleive that the Dearborn plant was very lax in this operation, not sure of the reason.

Any Mustang parts supplier should stock the factory assembly manual. There are several, each is focused on a certain area such as Engine, interior, and so on. They will be a valuable tool in your restoration.