I've measured the four downstairs living room windows,
and intend to order them 1 inch narrower than what we
installed in the dining room. This change will require
additional plywood shimming, but will obviate the need
to excise the central flange. Please confirm by e-mail
that I should place the order in this manner, 
or alternatively, that we should discuss the issue. 

I hope your day was not too difficult.