Other than the obvious styling difference - cruiser vs. sportbike, the Custom used shaft drive, which necessitated an "auxiliary" gearbox to change the direction of the power from transmission countershaft output to shaft drive input. While they were at it, Honda added a two-speed gearbox to this gearbox. So, effectively you get a dual-range, 10-speed model. 5 speeds in the tranny, and high and low range in the aux box. Had a little aux. gearshift lever above & behind the normal shift lever. Kind of a gimmick, really, but it makes the engine overall longer than the F model.
Otherwise, I THINK there are enough differences in mounting tabs, mounting brackets, etc. to make the conversion from C to F tricky.
For highway use, unless you use a windshield to block the windblast, I think you'll be more comfortable with the F's more lean-into-the-wind riding position.
Another thing to consider would be the 1000C / 1100F models. They were each one-year-only bikes. The 1100F replaced the 900F, and the 1000C replaced the 900C. Same deals with the two-range sub-trans.
Good Luck with your search.
Ditto on the 1100F.net forum. Lots of enthusiasts there.
Kirk
