I recently got one of these cheapo quanum 2-axis gimbals (which I might add had a faulty motor, thanks hobbyking...) and couldn't fit it to my DJI 550. I took michiwends to plate and reversed it and made some modifications to it to fit the Quanum gimbal. The top has also been modified with screw holes added.
The problem with the Quanum and the F550 is the spacing between the bolts which is 4.45cm. The curved slots in the F550 are not that wide, so the solution was so use michiwends plate and sandwich underneath and bolt up from underneath and besides some slight sanding to get the nylock bolts on the gimbal threads, it was all good.