Geo, if you mean can you make the window with Clearfix, then it might be pushing it a bit at that size. It'll probably 'skin' across OK, but I think it will look slightly concave when set. You'd also have to do this after painting the model, as Clearfix, and similar products, can't be masked.
Use the kit window, pre masked, and set it in place on a paint-free surface. Run liquid cement around the edges and, once set, re-inforce with tube cement, applied with a cocktail stick. Once set, re-paint around the edges of the window, where the clear part has a 'border'.