The Oliver 500 is a 850 David Brown. Parts for them are available from Case-IH. They were first imported in 1960. Is it gas or diesel? They are a little smaller than a 550 in horsepower. They have a dual plate 2 stage clutches, not a seperate clutch for the PTO like a 550. There are also 2 series of the Oliver 500 tractors. Serial number is on the right side setting on the seat and behind your foot. Questions?