Originally, I had planned to do a Half-track along the lines of my Manticore. However, other folks have already gone there, and done it quite well so I'm going to take a different tack. A ZSU-23-4 is an obvious choice, but the turret is a bit too modern looking to fit in next to my Medusas, the Ragnarok, and the Manticore.
Searching the list of Russian WW II vehicles, I find the ZSU-37, which has the right sort of aesthetics; with a bit of modification to the front of the turret, the quad autocannon from the Aegis Defense Line should fit nicely.
Or the ZSU-37-2 for that matter:
The turret will mount to this box, with a Razorback top hatch. I use a 25 mm base glued to the bottom of the turret as the pivot
Still need to add some details to the turret, but here's the general idea: