Got some work on there Matt!
It's a long, long time since I built a biplane, and I never liked the part where top wing and bottom wing had to be joined! The only thing I can suggest, is to make a box-jig from stiff card. That way, with a bit of luck, you should be able to align the wings for a test fit, and support the upper wing whilst the cement is setting on the struts etc. It will probably mean a bit of trial and error to achieve the correct shape for the jig, due to the positionof the engine nacelle etc., but at least it should go some way to making life easier.