I recently modded my Tatsunoko vs Capcom Arcade FightStick. (which is basically a Mad Catz Street Figher 4 SE FightStick)
The modding process follows exactly any SE FightStick tutorial I found online.
Here are some photos showing the inside of a TvC Stick just for your reference. As for resources, check out this video on how to mod an SE Stick, it does a good job outlining the process: http://www.youtube.com/watch?v=O4wDobtOmY0 and there are many other good ones on Youtube and help on sites like shoryuken.com.
The parts I used I purchased from FocusAttack.com:
Sanwa JLF-TP-8YT-SK Joystick
Sanwa GT Y Octagonal Restrictor Gate (I use Ryu and Dhalsim so prefer this gate)
Sanwa LB-35 Balltop Black
OBSF-30 snap-in buttons (I bought these on eBay, but would suggest getting these from FocusAttack.com)
I was happy to see that all the stock parts in the TvC Stick were generic Sanwa parts so all the genuine Sanwa parts installed with no problems.
One note about the joystick is that you will have to remove some of the adhesive "goo" that is used to keep the connections and screws intact. I just took my screwdriver and gently scratched it off until i was able to just peel it off by hand. Just be careful not to strip the screws or damage the connector when doing so.
Below are some photos of the stick:
Here is my TvC with just the Sanwa buttons on.
Here is the inside of the TvC Stick, the buttons just snapped in after I removed the adapters, the joystick is the stock MadCatz joystick with an rectangular gate.
Close up photo of the joystick, take notice of the "goo" (I think its just glue from the hot glue gun used when doing the wiring) around the screws and 5-pin connector.
This is how it looks removed. In addition to the 5-pin connector and 4 screws you remove, you will also have to unscrew the joystick ball to remove the joystick. It requires a flat head screw driver to keep the screw from spinning while you twist the joystick ball.
The new Sanwa joystick is installed with the new octagonal gate.
The TvC Stick back in my MAME/SSF4 cabinet.
The modded TvC Stick side by side with a stock TvC stick.
I finally mod'd the other stick with Sanwa parts. I couldn't stand playing on the stock TvC stick when I had people over; so it feels nice to have 2 sticks with Sanwa parts. I ordered the parts for this build from focusattack.com and received them in 2 days.
Good luck with your mod! If you need help, just post a comment below.