the ID number on the frame that Bill cites started at most plants by 55 or 6, every 57 I've seen has had it - the frame number will NOT have the leading model designation [3A in your case]

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 & Rust-a-holics Unanimous parking lot