I have heard that on some of miller's engine drives that the serial number may have also been written on the inside of the front panel. You will have to pull the outer wrappers to check and see. I have a Roughneck 2e that is missing the serial number plate also. Pulled the wrapper to do a litter housekeeping on the inards, and while at it checked around on the inside for a possible number. Unfortunately, my unit was not one of them they did this for. Yours may have it, and then it may not. A shot in the dark. Good luck.