russ74,
I wish Polaris did a better job of getting part numbers correct on the information that they distribute.
I took the liberty of adding some notes (in parentheses) to your post. This is based on todays factory parts database.
QUOTE
65 durometer kit pn: 2900187 (available) or single mount 3021242 (never a valid number)
90 durometer kit pn: 2900188 (discontinuted) or single mount 3021244 (one 65 durometer mount)
this comes from the install sheet that came from polaris for the pro-x