I suspect the "N" is for "narrow mount" or a Sho-Bud type of mounting - screw holes on the ends. The other type is the Emmons style mounting and it is a wider style with two holes on each side.
I guess the -N is is different from my &12 top-mount. Top mount means that there are two screw holes that go thru the pickup. It's a little narrower than the side mount model.
My Lawrence top mount is 1 7/16" wide.
The slot in the Sho-Bud is 1 1/4" wide.