Hello Greg, I think they come in two standard sizes, one about 5/16" x 1/2" and another thinner and flatter, probably 1/4 x 5/8 or so. You just use what fits best and sand to the contour if needed. The only thing, aren't most of your attaching points made of wood like shown in the photos above?
If you are using these nylon tack strips in (usually) postwar cars they work great and are far better than the original. But I am not sure they are available in thicknesses to replace wood in a Model A. Good luck, Todd