I took some pictures of the rig and posted a query on Russian Iron for help identifying the thing. I knew it was Russian, but that's about it. The guys over there identified it as an IMZ or KMZ (Irbit Motor Works or Kiev Motor Works) M72, a bike the Soviets first copied or made under license from BMW of the BMW R71. It's a 750 sidevalve motor, 6 volt positive ground electrics. The design was already 20 yrs. old in 1957.
It looked pretty rough and I wasn't sure what parts were missing. The tonneau cover was stretched as if a fat lady had used it as a hammock. It was evident it had been full of wet snow over a few winters. the tub was full of leaves and acorns and the seat was all mouldy. The rig was sunk into the ground up to the rims and the tires were all flat.
Anyway, after finding out what it was from the RI guys and doing some reading on my own, I was intrigued enough to call the number on the sign.