Yep, will get about 6C off the temps. Alternatively if you only have a few you can do the cooling mod (reverse both boards so the heatsinks both face outwards, then 2x120mm per blade blowing directly onto each heatsink).
Just fyi I was in the thought to do this and bought titan fans with 78 cfm. The problem with them was that the screws on both ends hit the fans. I was under the impression that the default fan used 103+- cfm . I'd hope all I need to do is find a nice way to space the fans out so they don't hit.
I still hope like you seem to hope that putting fans in that position will quiet these antminer and keep them cooler.
Edit FYI #2 rubber screws work but stink at being easy to put in so borrowing one of the screws from an unaltered fan may be necessary unless you can use the rubber and the spacers.
Any idea what fans will report speed to the antminer?
I think that the first fan it will be a little bit more noisy from the new one, cause its temp sensor is nearer in an hotter spot