The 'M' is what has me confused. I have had my hands on a dozen DC-1's over the years but this is the first I have ever seen with the M suffix. I was kinda hoping someone would pipe up and say that their 57 XLA had such a carb.
No 1st hand verification here, but for what its worth, ...... a friend whose info has always been gold says his friend has an unrestored 57 XLA with a DC1M.