That doesn't look quite like a bog disc. They typically aren't rectangular in shape. Could you get closer with the camera so we could look closer at the innards of that thing? Looks more like a sled you wouldn't want to sit on.
If I were you I would sand it down really good while looking for some identifiers. Names, numbers.....anything that can help identify it. I would take the time to do it because you could very well have an antique on your hands.
Good luck!