I took my 500AH, made and adapter/spacer and put one of the Manfrotto 323 connect adapter that uses the small 200pl plates. I did this so I could use the much smaller 323 connector than a much larger one on a couple of specialty scope stands, that actually clamp to a shooting bench. The work fine, I used some 1/2 " aluminum bar, 3/8 would have been fine. I just needed a spacer to clear the QD lock on the 323 connector which extends down below the mounting surface a little. It took some careful measuring, drilling a few holes of various sizes and tapping some of them for screws. I even drilled and tapped for a small allen screw that functions as an anti rotation lug. Another reason I wanted the smaller plate was so I could leave one on my Nikon digital camera, the 500AH plate was just too large and cumbersome on what is an average size for a SLR type camera.Hi,
the 500AH does not take Arca Swiss plates... and comes with a quite usable long plate (120mm iirc) which is normally able to properly balance your scope.
Of course other lengths are available from Manfrotto and 3rd parties.