We use this one, it provides really no adjustments aside from basic tilting but it's sturdy and holds two 32" monitors.
https://www.amazon.com/VIVO-Bracket-Horizontal-Assembly-MOUNT-VW02A/dp/B01CUSHR1O/
There are of course much nicer (and more expensive) options!
VIVO Dual VESA Bracket Adapter, Horizontal Assembly Mount for 2 Monitor Screens up to 27 inches, MOUNT-VW02A https://www.amazon.com/dp/B01CUSHR1O/ref=cm_sw_r_cp_api_glt_fabc_95C3QNDXGZF1DMNW53F5?_encoding=UTF8&psc=1
I had to mount it to a 2x8 and then mount that to the studs behind my drywall, that sucker is never coming out
I used this mount. Best one for large ultrawide monitors that I found. It's a heavy duty bar that mounts in the middle and allows for each monitor to be adjusted side to side. I ran the cables for each monitor along that bar, and they're bound together by sleeves with velco where they disappear behind the tower.
Definitely turned out as good as I was hoping.
What I used is technically not a wall mount, but a single vesa to dual vesa mount adapter. https://www.amazon.com/gp/product/B01CUSHR1O/
The plate is mounted to a 2" thick block of wood with 2" screws, and the block of wood is mounted into a stud via 4 4" long screws.
I thought I saw a stand and was thinking you'd just place the stand on the shelf. I didn't like stands for that reason - eats up desk space for stability.
If you'd like even more space, you could also mount the monitors on the wall with a wall mount. That would free up all the space the mount base would have eaten up.
Using these VIVO dual vesa mounts!
https://www.amazon.com/gp/product/B01CUSHR1O/ref=ppx_yo_dt_b_asin_title_o00_s01?ie=UTF8&psc=1
Monitor arm is the Ergotron HX (heavy duty model).
Love the Ergotron, it's an extremely well built (if expensive) arm which is very well balanced. Initially I had purchased the Ergotron to support an Odyseey Neo G9, but I didn't love that screen (I like HiDPI displays). So, I added a dual monitor attachment when I ordered the LG 27GN950s seen here.
One thing to note - I first attached the monitors to the support bracket before attempting to put the bracket on the arm. That turned out to be almost impossible by myself. They have a tendency to rotate off axis while trying to mount them, so I ended up mounting them one at a time. I don't recommend my approach, find a friend who can help or get an arm that's purpose built for 2x monitors
VIVO Dual VESA Bracket Adapter, Horizontal Assembly Mount for 2 Monitor Screens up to 27 inches, MOUNT-VW02A https://www.amazon.com/dp/B01CUSHR1O/ref=cm_sw_r_cp_api_glt_i_G53T1GA5ZEWC17ZT0P05
Use something like maybe? Attached to some kind of arm that points to middle of the car.
https://smile.amazon.com/VIVO-Bracket-Horizontal-Assembly-MOUNT-VW02A/dp/B01CUSHR1O
Or portable monitors on tablet mount, which has its own batteries.
I think something like this bracket in combination with a single arm stand would work. Could not find for 2x2 setup but you can also make a combination for that.
VIVO Dual VESA Bracket Adapter,... https://www.amazon.com/dp/B01CUSHR1O?ref=ppx_pop_mob_ap_share and I ran the cables behind the actual drywall
VIVO Dual VESA Bracket Adapter,... https://www.amazon.com/dp/B01CUSHR1O?ref=ppx_pop_mob_ap_share
Is a wall mount possible? (example)
I just found this which would solve some problems but you would need a really strong arm.
Are the 4 holes on the back not mounting holes? I can create a custom vesa adapter just fine so long as I know those 4 holes are capable of supporting the weight of the cintiq.
Edit: They are mounting holes. Judging by the pictures and what I can tell about the width of the cintiq, the holes seem to be 75-80mm apart from top to bottom. If that's true and it's 75, then a normal vesa mount would work.
As jerry-rigged as it sounds, I'm honestly hoping to try out one of these to adapt it to an ergotron arm.
Here. This will meet your specs:
https://www.amazon.com/VIVO-Bracket-Horizontal-Assembly-MOUNT-VW02A/dp/B01CUSHR1O
Use toggle bolts and you will be fine. Or use a studfinder and screw it into the wood beneath the sheetrock.