There really isn't a GOOD way to bottom mount that stick.
If you are looking for an authentic install of it, the TOP of the extra mounting plate needs to be about 1/16" below the top of your CP; and you'll need to fit another piece of metal to flush the entire assembly up with your CP top.
The mounting bolts should go through the flush metal piece, through the mounting plate, through your CP, and then have nuts on the bottom to hold the entire assembly in place.
The dust washer will ride on the mounting plate as is, to plug the hole between the mounting plate and the flush metal plate.
You might be able to get the stick "almost" high enough by routing from the bottom (IF you don't use the mounting plate, but I don't think it would hold in the long run--especially using MDF.
You'd also still need to rout from the top to accomodate the dustwasher, if you want it to LOOK authentic.
That would weaken the routed area even more.
I personally would (and DID) go with an
NOS Wico 4-way.
The seller in that auction is great to work with, and has a bunch of them for $24.99 Buy it Now.
I've bought a couple of those from him; and, while not completely authentic for Pac games, they WERE authentic for many other games.
The ball is bigger on the Wico's, it's not textured, and the shaft is longer.
The good side of that is that it will let you rout, or not rout, to get the stick height you want with them.