Yes, those numbers refer to the engine type. The 256 and 306 were the very early ones, up to around '73 I think. Then they changed to the 447 engine which is most likely what you have. The 533 was a long rod version sold only in Europe I think, so I doubt yours is one of those. Other than that, it appears you have a mildly modded Special on your hands. The U.S. didn't get an '84 model, '83 was our last. Canada did get an '84 though, but it's not any different really than the '83. I think Yamaha was just using up their stock of parts to make a limited model run for some markets. Your Canadian model did get the mag wheels with a drum rear, which is nice. In the U.S., we only got mags up to '81, a drum rear mag only on the '81 model, then spoke wheels after that.