Wheels originally designed for disc brakes are built differently than our vintage truck wheels. If you look at the back side of your wheel, you'll see it steps down in diameter twice from the bead to where the center section welds to the rim. That second step will be smaller (larger diameter) or non-existent on a disc brake wheel. I was able to put disc brakes on my '46 with the original 16" wheels with the use of spacers and a little grinding of the caliper, about 1/16" off the crown. My kit was from a different vendor but the one shown online for yours looks very similar.
Steve
