I'm trying to find the exact model of Fatty D I have. The bike is a 1998 F2000 that Bikepedia said came with a HeadShok Fatty SL,
but mine is a Fatty D (same color as the frame), so maybe it's a Canadian model (I live in Canada and bought it here).
My Fatty D is not disc compatible, has an air/oil damper and has 5 position damping.
On vintagecannondale.com the 1997 Fatty 70 has 5 position damping, air/oil damper and is not disc compatible.
The 1998 Fatty D has a coil/oil damper and is not disc compatible But
only has on/off lockout.
The 1999 Super Fatty D has an air/oil damper (like mine) but
is disc compatible (mine is not) and also only
has on/off lockout.
The number in the back of one of the legs is '2947 15 7FAT' but couldn't find any info on it, but I had better luck with the frame.