The rear rims are bolt on making it an industrial not an Ag tractor if it is 500B series it would be a 510B. The exhaust on the 500B series I've seen is on the left side outside the sheet metal. Pic is a 510B, note the exhaust and how the dash cowling is oriented on the back of the sheet metal, doesn't match, does it? You need to post more pics from different angles and closer. My money right now is on early 430 or 530.