standard model-year id

trying to id a motor that i picked up the number on the motor is 2f0-104284
i believe it is a xs650 se special 77-79 but cant be for sure any help i have used the tables and i think that is right but hate to order parts before i know for sure.

On the tables I use the 77-78 dates are the year of manufacture. As in August of 77 to July of 78 are all 78's .
My list shows your engine to be 78 SE, manufactured between August of 77 and July of 78.
The manufacture year don't coincide with the calender year because if it did new model years wouldn't be in showrooms till March or so. So they start building them months in advance.
On the engine parts except for a very few minor things all the internals from 74 up will fit. The 256 engines from earlier won't easily swap in. The European 553 engine parts won't swap in either. As long as you get 447 parts, no worry.
Leo

xsleo i just want to thank you for your time and help it has meant a lot thanks amanda