[BMF]

The holes were definitely cast in, although I don't think it's factory. There's no Triumph logos anywhere. Seems unused though.

 

[BMF]

Hi Stuart, it was definitely cast with the holes originally. Same w1040 part number appears on the mid-50s pre-unit manuals too.

But I think you are right. I'm going to tell everyone it came from a custom istd bike of the '50s 😉🤣