First off, I want to say I got the original inspiration for doing this from this instructable:http://www.instructables.com/id/Interfaces_for_Games_PunchOut/
I thought this was a great idea, but it was not really quite the playable experience I was looking for. I wanted something I could actually play as if I was punching the person I was playing. This led me to modifying my Slam Man Boxing Dummy to add arcade buttons I could punch.
Step 1: Unattach foam
The first thing you have to do is unattach the foam pieces from the head and torso of the boxing dummy to put the arcade buttons into. The dummy has these weird black plastic screw things that hold the foam onto the plastic dummy and you can pry these up just using a screwdriver. Once those are popped off, you can drill holes into the foam and insert the buttons. You also need to drill holes into the plastic where the button will go through to allow the wire to come out the back.
Step 2: The Back of the Head
One problem with a punchout dummy, is that you need one button for each side of the head, but in the NES game, punchout, it requires that you hit both the UP button and either A or B button in order to punch to the head. So in order to make that happen, I had to modify a regular arcade button by attaching together TWO microswitches so that when the button is pressed down, it actually is pressing down two buttons. This was actually easier than I expected. I used a couple screws to attach the microswitches together and then used hot glue to keep them in place in the arcade button.