I've been wanting to do this exact thing (replace the MSFF2 stick with the X-55), but I have no experience in either the required theory or practice, and whilst I can surely apply myself to the theory, once I start taking these things apart I know everything will need to go right for me to avoid a lot of wasted money (plus I think I'd feel guilty for killing a MSFF2 in prime condition).
Ideally, I'd love to do the stick extension as well, but the PeterP mod is so far above my capabilities that all this is just a pipe dream for now.
It's annoying; I just cannot go back to a spring centering stick unless I absolutely have to, but the MSFF2 stick is lacking badly, not only in buttons, but in the quality of the buttons. They are cheap and nasty, especially the feel of the trigger compared to the saitek sticks.
Congrats to the OP, by the way; it looks awesome.