Is the Fox made to fit a VFR750? If you don't know, there should be a part number stamped on the reservior cap, and callingemailing Fox would let you know if it would work or not. I looked into adding one to mine a while back, and they said they can still do rebuilds, but don't have parts to adapt them for other models anymore.
The F4i one has the same types of mounts, but I'm not sure about the widths of the bushings. You would definitely need a longer hose, and probably a different spring.
I have no idea whether or not the F3 one would work, though.
Having just removed my stock shock, the length was about 12.75 in. from center-to-center. It's probably actually 325 mm, but I don't have a metric ruler, and I was kind of hovering for the measurement. (IMG:style_emoticons/oldemoticons/rolleyes.gif) If you need other measurements, let me know.