I posted this sometime back. Check on the engine block as described below. IF it is the original engine, you should find your tractor's serial number.
Originally Posted by DJ54
I stand corrected of a second serial number location... Don't know what I was thinking...
Look on the right front corner of the block, just above the mag, or distributor drive. There is a flat boss just below the head with the serial number stamped there.
You may need to scrape the paint off to see it, if you haven't already found it.