Does your frame have the same rear end as this one?
It looks as if defconfunk (a member on here, who owns or owned this M1) has had an adaptor made up. It looks as if it bolts into the two holes that you mention, and then allows the use of a disc brake with an IS mount..
So I am having no luck whatsoever finding an adapter to fit my M1. I've talked with intense and HOPE , and a couple machinist. Can anyone assist where I may have luck
There was an M1 seatstay and chainstay on Ebay a few weeks ago, but the seatstay is gone now. Swapping those rear pieces would be the cleanest approach if they're compatible. Cloverleaf would probably know.