I'm considering swapping the inner ring on my SLX double chainset (M665) from 22T to 28T. I noticed that the newer M675 has a 40/28 option, so I figured that the 28T chainring from this set-up would work well on my slightly older chainset.
However, the Shimano schematic for the M675 chainset suggests that the chainrings aren't backwards compatible with M665. But I can't see how a flat inside ring with no pick-up points machined into it wouldn't be compatible, providing the bolt patterns match up (which they do, I think).
Have I missed something?