Engine number

[sparkywig]

Did a bit of engine cleaning today and found the number stamped on case under dynamo mount. However, it's not what I expected.

OVAL S3 :?

Can anybody shed any light on this?

 

[VWAIRCOOLED]

Maybe that S is a 5 and someone had that engine fitted in a 1953 beetle before? What sort of engine is it and whats the history?

 

[sparkywig]

Don't know much history of the engine, although I doubt it's that early as I've been told it is a 1600 single port.
I'll post a pic of the number next week.