KEF was engine used in U series tractors up through mid 1947. It had the one piece 4 cylinder head. In mid 1947 they went to 4 cylinder engine with 2 separate 2 cylinder blocks and heads.
Your tag is for a KEF engine, 4.2" bore x 5" stroke 4 cylinder serial number 565690. My list for serial numbers shows KEF engine production 1947 562681 - 565985 inc.
This engine was built in 1947 for the U series tractor