Had that thought myself, long before the Q2 diff appeared.
I asked around and have been told that there are big differences in the mounts of the two gearboxes, so that 166 gearbox cannot be fitted to an 147, unless you do a hatchet job on the gearbox mounts. Not sure about this though because i didn't try it.
Also used 166 6-speed gearboxes are really hard to find.