"I am sure 8' deep girders will be sufficient." Leon Moisseiff, Chief Engineer, Tacoma Narrows Bridge

"If you cant find 20' lengths of All-Thread then substitute two 10' lengths"  Jack D. Gillum,  Hayatt Regency hotel "Tea Dance" walkway designer.

"Sure, it's a little stronger with the window bonded in, but that small amount of extra strength is not required.  The fuselage is strong enough even with the big hole in it." Rob Wolf

Rob is correct that the static strength of the fuselage is determined without the windows BUT the windows do have significant "in plane" (npi) shear strength which will have an effect on the torsional stiffness of the fuselage. This, in turn, effects the natural frequency of the empennage. Making the fuselage less stiff by decoupling the window reduces the empennage flutter margin. Only analysis and testing will tell us by how much. Pushing the aircraft faster with bigger engines and making the fuselage less stiff  will eventually result in structural failure. I know of at least one IV -P that disintegrated in a 0.63 Mach dive.

Rob may be correct that the structural effects are negligible but his confidence is unsupported by analysis or testing. I doubt he has the factory's agreement on this matter.

Prudence, and experience, dictates a less cavalier approach to structural modifications.

Regards
Brent Regan