I recently picked up an M101A3 from Camp Pendleton in SoCal. It used to belong to the USMC. The data plate on the bed is pretty much scrubbed clean. The data plate on the trailer frame is faded, but the VIN and manufacture date sections were stamped, and so were readable.
For my SF97, I listed it as an M116A3, which is what the frame is, and what the data plate that has the VIN says. The VIN section of the M116 data plate was stamped "S/N 9999 USMC 999999". The 6 digit number in the VIN is what had been stenciled on the side of the bed, but GL or someone went happy with the spray paint on *ALL* markings.
So, I put the "9999 USMC 999999" on the SF97 form request. GL accepted it that way, and issued the proper forms to me. CA DMV did the VIN verification, and had no issues with it.