Same stroke, same bore,same displacement.
Ultra is case reed engine, as is the XCR.
'96 Ultra engine is EC68PL01 (SP & SKS) or EC68PL04 (RMK), '98 XCR 700 engine is EC68PL60.
Check out this site for parts info:
Browse Once you find the part, click on "USAGE" to the right of item description to list other sleds where this part is used.
'96 Ultra has an oil reservoir for lubricated water pump. Later engines did not.
Can't answer if it is a direct fit as I've never done it.