Engine ID plate should be on flywheel housing tinwork just to the rear of the carburetor. The metal plate used back then was riveted on higher up than the decal shown on Page 5 of the manual linked below.
Original 140's had a Kohler K301 12 Hp engine, it was updated to a K321 14 Hp engine at tractor serial number 10,001, in 1969.
If the 12 Hp engine was in need of replacement, often it was replaced by the 14 Hp version. If a shortblock was used, and the tinwork reused, there'll be a 14 Hp engine snuggled in under the tinwork still bearing the ID tag of a 12 Hp.
Also, the block casting of at least some engines was marked "K301" or "K321" on the face of the casting in the output shaft area.
You can see "K301" above the oil seal in the photo below.