Thanks for the comments,
Erik, yes it will have Russian markings. Probably something seen in the Chechnya conflict.
Roel, the gun is an Azimut production. In fact, it's a combikit with two plastic sprues from a brand called Scale (!), resin, PE and metal parts from Azimut.
The instructions are a mix of original ones with Azimut mods. So there are some mistakes and omissions. Nothing a good documentation can't fix.
The BTR-D is from EE. Not a bad kit but quite soft details and a hide and seek instruction leaflet !
Mike, I intended to do this one before I knew Alanger was on the starting line too

Having seen their BMD-2, I can tell it's just a reboxing of the EE kit. So should be their BTR-ZD including the gun.
Azimut sell the gun asa separate item. Check their site and in the search engine type ZU23-2 and you'll have the reference.
The gun mount is secured to towing eyes with tightened ropes. I have some pictures but they don't show both ends of the securing system.
They can help anyway. The mount rests on three bits of tree trunk and not directly on the armor plates.
Olivier