YES, you can fit 2 full size moto's in the s/box w/ the gate up. Did it for two years before cuttin loose the smoker- Ancient Moto secret trick.......
You angle both wheels to press against each other in the front/cnter of the bed( left bike turned right, right bike turned left) they hold each other up-then swing the rear wheels out all the way to the inside of bed and the gate will close-
FYI- this trick will only work in a chevy/gmc s/box, I dont know why.