Your already onto the checking of head and base gaskets but the other one to consider are read valve gaskets and exhaust flanges but you always have to wonder if the part numbers are correct as there are a lot of common mistakes in the many web sites and Zedder etc.
It does look like though that the power valve mechanisms seem to be the same over a few years but the power valves themselves are one year only along with the cylinder suggests to me that they were more likely changing the porting specs more than a major revamp.
Kawasaki did this also in the late 80’s and early 90’s, they often changed the port tracts and the scallop shape in the power valve otherwise the cylinders were the same.
I have no knowledge of your model but I would assume you could use a different year if you get the matching power valves to suit.
Beware though, my advice comes with no care and no responsibility