If it looks like this and falls in that range of serial numbers,I'd say it is. The 600s had a whole different set of numbers. The 600 numbers seem to overlap the DB 990. I can't find a serial number listing for the DB 850,not on here or even on Tractor Data. Those numbers for the 500s show a few more than the 1648 if they were totally sequential,but I'd think if they overlapped,there would be a heck of a lot more numbers than that. I'm wondering if the OA designates it as an Oliver for sure?