rear sprocket swap question

[stillwater]

Looking to increase top speeds & drop rpm for interstate travel on my XS400-2.

I found a Sprocket on eBay, seller says it will fit 1980, 1981 Yamaha XS400
Would it fit a 1979?
Or, how could I get it to fit properly?

 

[stillwater]

Thought I would add that ones I've found supposedly also fit the earlier XS250 and XS360 models, some of them anyway if that helps.
Wondering if the '79 had a one-off setup or something.

 

[CaptChrome]

My understanding is that the rear sprockets on the 80-82 bikes had an "offset" to allow the chain to clear the fatter profile tire on the 16" rim. The earlier bikes with 18" rims should have a flat sprocket. I don't know if an offset sprocket will work on the flat sprocket bikes, but I a pretty sure that using a flat sprocket on a 16" rim bike will cause some chain wear on the tire.