I went from a flying 9A to a 9. The reverse should be similar, although I think it might be a bit more difficult overall. You need a new engine mount, gear leg weldments (if going from 9 to 9A), and gear legs (3). Need to remove the tailwheel & spring (easier to leave the weldment in place unless you are still building), and probably move the brake lines around. Also need to cut holes in the fuselage for the gear legs to mate with the weldments and a slot in the cowl for the nosegear leg. Depending on configuration and whether there is interference with the nosegear socket on the engine mount, you may also need to shift a couple things around on the firewall. Adding steps would be optional.
Probably a month or two worth of work (on a part-time basis) but could be done in two weeks if you worked on it pretty hard. In my mind, the most difficult part is going to be adding the gear leg weldments because of the need to pull the wing bolts and working in that confined space.
Cheers,
Greg