I like the frame on the 3rd gens better than the 2nd gen for strength and stability. I would guess that no one has done it because the cabs are nicer in the 3rd gen. Why not find something unique to set on it like an old 2.5 ton truck cab or something that's easy to find in Estonia?
Just a thought, but if the rear cab mounts are directly above the frame, you could just do something like a nutsert into the frame to bolt to.