I have seen several Gus's with windows and there was one thing I never was entirely sure about until I could see it myself. Gus most of the time cut the windows for the butt sleeve from a wood that had 1 main figure, like 1 bird's eye in it. It was weird to see and especially read but as far as I can tell it is pretty much true.
So if the cue has tons of figures in the windows you may be on the wrong track but this only - of course - shouldn't be the deciding factor.
As someone has said it already, I think that you should look at as many pictures as you can, check out the black joint ring heights below the stitch rings - they appear to be taller than on other Gus-like cues from the past like on JW's for example.
The length and the evenness of the points is also a major factor, you don't really see short points on Gus cues or forearms.
I wish I could tell you more. Anyhow, if you won't take it for 1grand then I will, a nice old windowed JW is worth a grand too.
I would take it.