ok this step is time consuming its called pad hacking.this can also be easier to get a xarcade tank stick strip it and install it.but my way is cheaper and a little better in my opinion.i made a video tutorial for this step you can see it here...
once you have that part done we want to put the buttons through the art work and plexi and screw them in place and install the micro switch's that came with them.if you tape the art work to the plexi in the corners with clear tape you will get it perfect.(see pics below)
next we wanna mount the controlers to the bottom of control panel and wire them up.(see pic below)
to wire the buttons use the ground from each controller and daisy chain it to the ground of every micro switch.then take the button wires and wire them to each positive of the microswitch's.(see pics below)