I have a new 300mm lens for my Wista 4x5 field camera. It is a heavy lens and requires full extension of the bellows (12") and a lens extender (~2.5"). This set up does not function with my one screw stabilized Slik, or with the Manfrotto head just tried out in a store. The front weight of the lens/bellows causes a slow slide of the lens towards the ground. Total weight of the camera/lens is 10 lb., with most of it coming from the lens.

This camera has 2 screw threadings for mounting, placed front to back, 3.5mm apart from each other. Are there tripod heads that allow screws in both locations at once for added stability?