If I may offer some input, if you look at the next to last photo and the bottom plate, you'll see on the far right the indent in the locking plate that is required to use IXMOO cassettes. Early M6 models would accommodate the cassettes without modification. Later ones require an early baseplate to work. So, I believe this M6 will indeed accommodate the IXMOO cassettes.
There’s an additional notch that needs to be checked where you insert the film into the camera. If this notch exists it will block the IXMOO from being inserted. Later M models added this notch to accommodate more electronics I believe.
Leica M6 Excellent Condition 
