People ask about upgrading the X-Arcade sticks fairly often.
I swapped in a pair of Sanwa JLF-TP-8T sticks yesterday, so I thought I'd post some pics and let them know what they are getting into.
JLF, JLW, & X-Arcade mounting plates:

JLF plate on top the X-Arcade, X-Arcade on top the JLW plate

When people ask about swapping in Sanwa JLW's the response is usually "widen the holes and either route out the x-arcade case or put a block under the plate"
After having the parts in my hands, I'm gonna say widen the holes and trim the edges of the mounting plate. It's easier to work on the plate than work inside the case. You also won't lose any height that way. This is about how much you'll need to widen the holes: (and how much you'll need to trim off the edge)

The JLF's aren't as simple. I had planned to give the X-Arcade base and JLF plate to one of my machinist friends and have them make an adapter for me.
The parts sat on the kitchen table for about a half hour before I got impatient and decided to attempt it myself. I figured I'd make a temporary solution so I wouldn't have any down time.
Warning: The following was done by an impatient amateur. Results not absolutely perfect, but turned out pretty good! Attempt at your own risk.
I had some scrap 1/4" ABS plastic in my shed, so I used that. To make a template, I taped the JLF plate to the front of the X-arcade plate and put it on the scanner. Then I scanned it, printed it out at the same dpi, & made sure it was true to size.

Then I drew crosshairs from the center points of the JLF mounting holes to get the center of the joystick opening.
Then I cut it out, taped it to a piece of ABS plastic that I had cut to the X-arcade plate dimensions and used a punch to mark the center points of all the holes that needed to be drilled. I figured as long as the spacing between holes was correct, it didn't matter how ugly my plate was.

Holes drilled. Joystick mounting holes countersank; these were later redrilled to make the countersink deeper. The original screws allow for hardly any thickness at all. If going this route, it would probably be better to get longer screws.

Mounted:

The JLF's snap together, so the restrictor plate & switches can be removed in just a few seconds, making it easier to tighten down the nuts.
The Sanwa bat tops are smaller than the x-arcade:

I tried to remove one of the x-arcade bat tops to see if they could be made to work on the sanwa, but was unable to separate it from the shaft.
The x-arcade shaft covers can be made to work with the sanwa, but they must be cut down. They ended up just under 1.25". The sanwa dust covers will not fit around the x-arcade shaft cover.
The x-arcade stick needs the shaft cover to hold it up!
If you hack your original shaft covers, your x-arcade sticks will no longer be useable.
The dust covers that came with my JLFs (from Lizard Lick) are just barely big enough to cover the hole in the x-arcade control panel. If the centering of your joystick is anything less than perfect, the hole will be visible when the joystick is pushed to the side. I'm not sure if they are sanwa or not, they don't say sanwa on them like the one from my JLW does. The one that came with the JLW is larger and won't be an issue.
Height difference, original, Sanwa (using 1/4" ABS to mount):


It's a sleeper:

So here's where I'm supposed to wax ecstatic about how great the JLF's with the octagon restrictors are...
eh...I'm not as thrilled as I thought I'd be. The action is soooo light that they just don't feel like arcade equipment to me. (at least not from my day)
With the x-arcade sticks, I rested my hand on top the stick and banged it against it's limits.
With the Sanwa, I rest my hand on the cp and work the joystick with my fingertips.
They feel "dainty"

I'm wondering if I would have been happy just adding cherry switches to the X-arcade stick or using IL Eurosticks, which drop right in.
The octagon restrictors are making me more conscious of the stick position. I was able to pull off fatalities in MK that I had trouble with before.
I think it's even helping on 4-way games because I'm so conscious of where the stick is. They feel like training wheels. Once I'm trained, I think I will move on to a round restrictor plate.
I may still have a metal set of mounting plates made.
If I do, I'll scan & post it so it can be made into a good template.