Ted, I would glue the fork on and let dry good, I also like to have the seat installed, so I know where it is in relation to the fork.I dampen my leather with a sponge, I like to form a border with dividers set anywhere 1/4 inch to 1/2 inch from the seat, I will also use the horn as border and the front of the fork, then I will take a stylus and blend these border lines together with graceful curves. Then I will layout the pattern flowers and leaves with a stylus. I have heavy draw down so I will tilt up against my bench so that I have somewhat flat surface to tool on. It is not perfect and the tooling tends to be spongy surface compared to tooling bench. Some saddle makers have hydrolic chair with a locking pivot ball, that allows them tool in just about any postion. Hope this helps.
Steve