Probably the reason no one is replying to your question, is this question comes up ALL the time.
Bottom line is there is no one best solution for a control panel. Depends entirely on the maker's personal preferences, and what games they play.
Do you play q-bert and such a lot?
You can program the U 360 to do diagonals only. Problem is it can't detect what game you have loaded, so would require you to manually launch the configuration software and change its configuration based on what game you plan to play. It's a double edge sword, because if you don't change game-types often, why have a configurable joy, but if you do change game types often, then having to re-configure the joy in a separate program prevents it from being guest-player friendly.
On my CP I mounted a sub-minture 4-way joystick at 45 degrees, and love it for q-bert. It's small, so doesn't take up much real estate on the CP, but works as good as the full-size sticks do. My other two joys are a previous generation of the current Omni Stick Prodigy. I love them. Guests intuitively understand how to switch from 4 to 8 way, and I can just look at their stick to know if they have it right or not based on the position of the switch.
The Mag Stick Plus is nice because the player can switch from 4 to 8 way by simply pulling up on the stick (sticks that require access below the panel aren't as useful for guests on your machine, as they require below-panel access and technical understanding). I've never used the MagStick so can't say how good they play, but I have great faith in Ultimarc, so I would guess you have chosen well.
Honestly, I can't imagine why you would have predrilled your CP before you knew what sticks were going in there. They aren't universally interchangeable. You may end up having to redo the CP if your stick choice doesn't fit.
Two trackballs? That's a giant real estate investment on the CP. You'll end up with a franken-panel that plays nothing well. Trying to use one control will bump/interfere with other controls etc. or be uncomfortably placed. Biggest mistake of new builders is trying to do it all, making a panel that does nothing well.
My advice.... focus. Consider multiple cabinets, if you have the space in your game room.
If you really want to go hardcore... consider a rotating control panel. Few rotating panels have been done well, though.
Rotating control panels are a whole new level of technical challenges to make them work. For the tron sticks and yokes to fit, the whole assembly has to be asymmetrical with the pivot point off-center to give the tron sticks the most room, and the standard joys the least, and allowing the yoke to hit, thus preventing 360 degree rotation (to prevent endless wire twisting until it breaks). It can be done, though. I've done it. If you want to go down this rabbit hole, I can help you. It's not for the feint of heart, though. Since you want to do multiple trackballs, which are low-profile, a rotating panel may be ideal for you though.
Edit to add:
>The Million dollar question is this. If I mount the joystick properly, can I mount the 4-way restrictor plate diagonally on either the U360 or MS+, or do I have to mount the stick diagonally?
The U360 is programmable to 45 degrees no matter how you mount it (but remember has to be reconfigured when you change games).
You would have to mount the MS+ diagonally to get the diagonal 4-way. You don't want to do this. There are no games where a 45-degree-rotated 8-way is playable.
Edited by Gatinho (01/07/19 10:20 PM)