Used JD FEL incompatible with X720?

A rare used FEL is sitting on my dealer's lot after a trade-in (I believe it is a JD 45 or could be a 40). I came in with an older model JD 455 with a snow blower and the dealer plans to sell it altogether; he told me it is not compatible with the X700's.
I have previously inquired about the JD FEL 45 and have come close to pulling the trigger so I was very interested when I saw this used one.