There should be a serial number plate near the seat on the rear end hump and a number cast in the block on the right side, top right corner just under the head. The yesterdays tractor sight should help you deciper the year along with any other information you need. I have an "A" that I mow with. I had to put a different engine in it this spring due to rust and sediment build up in the block around the sleeves, it rusted the block out. There are water pump kits available to help with cooling and to keep the sediment from settling. I guess I can't complain about putting in a different engine though, the tractor have been in operation for 64 years!