Id like to be wrong but i dont think much stuff made it back to Japan
most of the stuff from Europe ended up in the English channel along with the luftwaffe
Back to your frame though who knows
could be a factory special
any numbers on the frame , that arm looks like steel protoype of that pds arm on your 125C .
Your in the hot seat
what was the Japanese domestic mx scene like in the mid to late 70s ? ive seen videos of earlier times in japan, it was amping in the late 60s early 70s