Thanks for your reply.
I agree with the possibility the last number was not stamped. I also entertained the possibility that the faint 4 could also be a very faint double stamped 2 (missing the top 1/3 of the character and raised higher than the rest)but I really had to use my imagination for that.
So I guess this engine is another orphan with a unique stamp. In your opinion what is the best use of this motor?