Yup, I was eyeballing the Manfrotto 460MG as well.
Being magnesium it weighs a paltry .95 of a pound, but only supports 6.6 pounds. With a 4x5 Wista, wouldn't it be doable..? The head would be rated for 6.6 pounds at its most extreme range of movements, so wouldn't it be solid with a field camera that's used pretty close to horizontal most of the time, especially if the camera and lens are well below what it's rated for..?
Note to self: Turn your negatives into positives.