I too have had problems putting new plastic on old GG bikes even with several "good used" subframes to pick from. Large tanks make matters worse. The subframes can be bent back pretty easily with a 2x4, piece of pipe or jack handle or you can put them on the floor and stand on them to bend them back into shape. 1) You have some adjustment with the slop in the subframe mounting bolts/tabs. 2) You can also elongate the mounting holes too. 4) You can drill new holes in the airbox and/or add some spacers. 3) I needed to move the seat mounting tabs further back to make everything fit on our 03 DE300.
If you have aluminum welding capability, I have a couple that need tab welding and I am in the burbs of Chicago if that saves you some shipping.