I don't think that the American Y Blocks have an engine number.
My 55 has no stamped number anywhere and for the purpose of licensing a number will need to be allocated, unless I stamp the chassis number on the block.
A 56 I recently saw licensed here in WA didn't have an engine number either and had some numbers punched on the gasket surface of the valley cover which we used. These did not seem consistent with a Ford Number.
The Aus/Canadian engines are all stamped in two places. Just below the front of the left head and behind the starter motor.
No such luck with the American.
My suggestion is don't worry about it if there are no numbers visible. Either put your own number on the block or let the licensing authorities allocate a number.
Regards
Rick - West Australia
Do Y Blocks Downunder run upside down? Gravity Sucks!!