Thanks for the kind words.
I spent a lot of time modifying that Momo knob, but you could make it easy on yourself by just picking up a shift knob that is already equipped with a switch. There are several on the market that have momentary buttons - Hurst, among others, makes a couple different designs. One of those would give you a nearly plug-and-play installation.
I would have gone that route myself, except I wanted a knob that cosmetically matched my E-brake handle, and I wanted to keep the wires completely hidden. That project was a couple years ago, and I didn't record any notes at the time, so I apologize if my response is little vague. I used a Radio Shack #275-644 pushbutton. This is the part:
momentary contact pushbutton.
I used the nut that came with the pushbutton to secure it to the top plate of my shift knob, but the knob I used is a multi-piece design, which made the modifications for the switch easier than they might have been. If yours is a solid piece, I imagine it would be easier for you to drill the knob and either tap it and thread the switch in from the top or drill a large enough passage to just slide the switch in and secure it with adhesive.
Getting the wires to exit out the bottom may or may not be possible, depending on the shift knob you are working with. If the neck of your shift knob threads onto your shifter handle, and you want to keep the threads, you'll probably want to drill the side of the knob above the threads and exit the wires there.
The neck of my Momo knob wasn't threaded for installation on the shifter handle. Instead, it was designed to secure to the handle with supplied Allen screws, and I was able to use this to my advantage during the pushbutton mod.
I had already learned with a previous Momo knob this set screw arrangement isn't acceptable, because the knob continuously works itself loose, and it never really sits right on the handle, even when it's tight. That previous experience had led me to come up with a workaround. Specifically, I found that I could press a piece of ASTM pipe into the neck of the Momo, and then tap the ASTM to the correct thread for the handle. That way, I could thread the knob on just like the factory part.
This workaround turned out to be doubly important in modifying the new Momo. I hogged out a channel just large enough to accommodate the wires along one side of the knob's central cavity and recessed the wires there before installing and tapping the ASTM. This way, the wires would be coming directly out the bottom of the knob, and they'd be completely concealed once the knob was screwed into the boot.
Most Momo shifter boots are equipped with threaded collars that enable various Momo shift knobs like mine to be screwed into the top of the boot for a very clean appearance. Since I had routed the wires directly out the bottom of the knob, inside the perimeter of the collar, I was able to keep the wires completely hidden once everything was all buttoned up.
Routing the wires down to the REV solenoid on the transmission isn't any big deal. I just cut a hole in the outer shift boot (the one with the metal plate that secures with 4 bolts) to make a passage for the harness.