12-27 No problem If its 52/42, 39/53 might just be on the limit. I don't think you will be able to use either the 52 or 53 ring with the 27 sprocket though, but will work with a 25 sprocket
Yup, that's what I was running.
The 39x12/13 rubbed on the inside of the 53 (as they do) so I didn't use those ratios.
53x27 worked, but who the he'll would run that!