Install just the top half of the filter box first (all bolted up), then slide the bottom half in and attach it to the top half. If the airbox boots to carb body are giving you fits they may be age/heat distressed and may need replaced. Reconditioning them might help (search "wintergreen") but I know the new airbox horns made my 750K model much smoother to install.
Congrats on the new aquisition!