I'm going to go with a 2 player cab because I'm mostly into fighters, not 4 player beat em ups.
Now, after reading this on the unicade site, I have a barrage of questions. I hope this isn't too complicated for 1 thread, but I figure it would be better to keep this thread alive than to create multiple ones with simple questions.

The next objective was to decide on the controls. I knew I wanted a do-everything control panel but I knew there was no way I was going to fit it all on one control panel. I had seen some examples of detachable and rotating panels on the web but I thought they would be more trouble than they were worth. I thought of some of the games I like to play that have special controls: Ikari Warriors, Heavy Barrel, Smash TV, Centipede, Tron, Xenophobe, Tempest, Arkanoid, Star Wars, and some others. I came up with the following list of controls to play all of these games properly: rotary joysticks, dual joysticks per player, a spinner, a trackball, a yoke, and a pistol grip style joystick. The problem was that I knew I wasn't going to fit all of these controls on one control panel so something had to go. What I decided upon was to have a spinner and trackball in the middle of the control panel, and dual joysticks for each player, one a rotary joystick and one a top-fire joystick. This seemed to be the best possible solution since I could still play Tron without the pistol grip joystick by using a top-fire joystick and spinner. The only real draw-back is having to play Star Wars with a mouse instead of a yoke.
I've decided to take a similar approach, but I have a few questions. In this image, there are 2 top fire joystics.

I haven't played Tron in a while and cannot remember if 2 joystics are necessary or not. Also, I noticed the 6 button layout is sort of crooked. A lot of other control panels are modeled like this, why is that? Why is it not straight across like the standard Capcom layout? And finally, Scott mentions he designed a circuit to change the way his joystics perform as stated below.
The middle two joysticks and top-fire buttons are wired the same way as the buttons. The outer two joysticks, P1 left and P2 right, are wired to a circuit I designed to allow me to select between 8-way, 4-way, and diagonal modes. The circuit works via a switch mounted on the control panel. When the switch is in 8-way mode, the signals that come from the joysticks pass through the circuit unaltered. When the switch is in diagonal mode (i.e. Q-bert mode), a logical AND function is applied so that only the diagonals are registered. When the switch is in 4-way mode, P2 right, which is a 4-way joystick, takes over the inputs from the P1 left joystick The inputs normally received from P2 right are disabled.

Does the IPac or JPac from Ultimarc have this option included? Is this only possible with a keyboard hack? If it is possible, how difficult is it to do? The reason why I ask is that it seems this project is somewhat older than others I have looked at. I figured there may have been some new, easier way to accomplish joystick control method switching.
If it is possible to easily duplicate this control panel layout, I will probably try and duplicate it in my machine. I really like the idea of hitting a switch to go from 8 way, 4 way, or 4 way diagonal. Do you guys agree that this is a good idea?
Once again, thank you all for your time.