Yup, that sticker is the serial number. Those F100 engine plate numbers seem to fade or disintegrate early. I had to use that sticker to get my engine insured a few years ago but I verified it with a dealer before quoting it to the insurers. I think the block does have the serial number stamped on it but itís normally effectively inaccessible. I seem to recall seeing it behind the inlet manifolds when I had the carbs off or maybe behind the regulator/ rectifier and it did match the black sticker. The block is from the FJ1200 bike engine which is why the serial stamp winds up being inaccessible.