I use the Manfrotto 3421
http://www.bhphotovideo.com …3421_Heavy_Tele_Lens.html
Manfrotto calls this a Heavy Duty Gimbal Type Telephoto Lens Support (Quick Release).. They have called it several names but, it is the same mount.
I use it opposite to the way Manfrotto has it set up in the picture. I mount the camera "on top" of the interior gimbal support which hangs in a "U" shaped configuration within the exterior "U" shaped support.
I love this mount using my 400mm f/5.6L as well as my 300mm f/4L and 1.4x IS. I can balance it so that it will stay still if I take my hand off the camera but, will move with finger pressure.
I shot a hydroplane race with the 400mm f/5.6L and a 30D on the 3421 Gimbal Mount and it was very easy to follow the 150+ mph boats.
The mount comes with an "Arca-like" quick release which works like the Arca but is not interchangeable. The mount and plates are larger.
When I purchased the 3421 last year, it was very inexpensive (It was under $100 with lens plate) but, has increased in price almost 50% since I purchased it. It is still a worthy gimbal-mount candidate but, I think that at today's prices, I might investigate the rip-off gimbal mounts on eBay these days.
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