Dave, I have done research at the MHS for about thirty years now
and have some idea of the lay of the (NP) records. The admonishment to "check on the hours" the library is open is a good one, and should be heeded.
The drawings are sorted by a five/six digit drawing number. The drawing number is found in another area of the Mechanical records. This other area is time well spent as it give and equipment and vendor run down. I have some numbers recorded, however to walk in cold, it does take a while to get the routine down.
Once one does find the full size drawings, I'll admit, rolling them out, the wax crayon like smell is quite intoxicating, and those who have done that can imagine this right now.
Send me a post off line with the cars you are looking for. I have a convention to put on this summer however will try to help you out.

Jim Dick - Roseville, MN