It looks like they may be the same now.  The 650k, 750k, and 850k look VERY similiar to the D75, D85, and D95 in specs and in pictures.  I did a parts search and the 650 and d75 use the same fan belt.  Here are some pics from the websites.

I have a Case 1150E and an old 1150 (1974 vintage) and they are both reliable machines.  I can get parts from my CIH dealer (he has the Case skidloader line) or from a Case construction dealer.  I can access parts books online for both machines at www.casece.com .