While the Zu-23 does appear on the ZJ75 vehicle in some videos of this Technical on YT-
Sergei on Landcruiser
http://www.youtube.com/watch?v=csUhgHa7xJIAs you can see it is really a case of the man carrying the horse as the recoil alone rocks the vehicle on it's springs, making accuracy all but impossible even in a supporting fire mission.
This video-
Nissan Longbed 2ton Truck, AAA mount
http://www.youtube.com/watch?v=oDwMPGn80VQShows a more appropriate mount for the ZU-23 in it's original anti aircraft mode.
This weapon-
ZPU-2 on ZJ75
http://www.youtube.com/watch?v=R4UMSWFUVVwIs far more likely for the surface support mission. Note that the bed is very shallow and appears to have been built up even more so that the gun rests on a flat black platform and only the upper edges of the bed have had to be cut down to provide full, 360`, traverse.
This is why the Landcruiser is so popular as a gun truck in comparison with the Toyota Hilux etc. Indeed, for those interested in the latter Meng release, be aware that the only way they can get the ZPU-1 to function is by taking the gun trace legs and attaching one at each corner of the bed with the third anchored to the front of the bed and the gunner sitting several feet up in the air.
An aftermarket company is missing a real chance to make a profit here as the 14.5mm HMG looks so much better on the smaller Landcruiser than the 23mm cannon does...