Sheldon says typical chainring spacing is 5 mm. That means the outer ring sits at 46 mm with a 109. You need to lose 4mm on the right to get it down to 42mm, I guess... Are you sure your cranks take a 109 when used as a road double?

FYI a 107 works with my 600 cranks to give 42mm-ish chain line on the outer ring. Probably more like 43. However I had to file 1.5 mm off each of the inner horizontal chainring tabs for clearance against the chainstays.