'58 VIN alternate location question

[Old Crow]

OK, customer is getting ready to plate his truck.
I took over this business in the middle of the build and when I went to his file to locate the VIN tag so we could put it back on...nothing.
He bought the truck from Mississippi and brought it to us in Arkansas to build.
He, apparently has no paperwork because he called me(from Texas, where he lives)asking me to locate the VIN.
I've got 2 Mississippi license plates...a standard plate and an antique truck plate, but no VIN tag. I've located the holes on the front of the driver's door jamb where the tag should go, but no tag.

Now, my old F-100 has the VIN stamped into the frame in addition to the tag, so I tried looking on the frame and can't seem to find a VIN anywhere.

Is there a number stamped on the frame, and if so, where is it?

I guess the alternative would be to get my buddy the sherriff to run the plates and see if he can come up with a number, but I hesitate to drag law enforcement into this unless I have to.