[Tinker]

Some parts from 38-41 will work on a 39.

38 and 39 are really the closest outside a few things like the inside of the door (38 was a cardboard insert, 39 had a steel insert/cover,

The dash has some differences. Ash tray in the middle of the dash in 38, not in 39. Front Window regulator was a "t" in the front facing inward in 38, 39 was a round knob on the top of the dash. Gauges.

Then of course the obvious hood latch and grill differences.

For the most part everything else is interchangeable between the years. Well they will all work really but if you want it one year or another then you wouldn't want to interchange items.