You are really pushing it on the trunk size.
I would say it will work, but you will be increasing the "static pressure", and you may end up with some noisy grille outlets.
Your furnace is pushing 1200 cfm which is good for 3 tons of AC.
Your 2 ton AC system would only require 800 cfm.
The rule of thumb for AC is 400 cfm per ton.
16X11 is right on the line for 1200,.............keep in mind this is "ID", not "OD" measurements.
If you have any way to use round duct a 16" round will do you for around 1400 cfm. 14" round is the equivalent of your 16X10 rectangular.