Technical Anyone seen a flathead number like this?

Looks to be M90:4
I’ve looked at van pelts flathead list and there is nothing like this number. M =mercury?

 

Probably a casting control number whose actual significance has been lost to the sands of time.

I blame the Corvette "matching numbers geeks" for this desire to find something meaningful for every symbol stamped or cast into a part.

 

Flathead have casting numbers such as 59,8ba etc etc on the bell housing.this one has this code which I cannot find.
Looking at purchasing this motor and want to know what it is. It’s a 24 stud 59 style block.

 

Itsa prewar block. As said, we will never be able to decode that number.