frame numbers started in the TF series - the leading model ID is never on the frame rail [the '3A' part] - and it was likely 'hand stamped' with the aid of a machine, the frames were stamped when the frames were assembled, the door tags were stamped to match the frame number
a friends 56 frame

Bill

Moved over to the Passing Lane

"When we tug a single thing in nature, we find it attached to the rest of the world" ~ John Muir
"When we tug a single thing on an old truck, we find it falls off" ~ me
Some TF series details & TF heater pics