Well, my 350 CF came with this Chinese bracket, and if it proves anything ... nobody got it right. Hasselblad made this lens without tripod mount provision, and I order to get it in a right place, it would have to be integrated in the lens body design. Since Hasselblad opted out of it, and in my opinion that was a grave mistake, this is not hand holdable rig for crisp shots, the only place an off-brand collar could mount is only just in front of the shutter adjustment ring, which is too far forward. With collar used, balance is significantly better, but end heavy. With camera mounted on its tripod foot, it is much more front end heavy.
But we're talking still quite a bit of weight, and collar placed on lens barrel surely NOT designed to withstand this kind of stress, I'm not sold it's a good idea to use it, at least not as in leaving this rig on a tripod hanging out there for long periods.
Besides, the collar is as spartan as it could be, so it's a bitch to swing the the king within it, if one were to shoot 645 back and needed portrait orientation. Of course the design could have been far more intricate and have built-in rotation and click stops etc. I don't think there was ever a market for such a thing. So collar is well made, but as basic as it could be.
I'll take some photos of this rig once I find 3/8 to 1/4 adapter (collar has 3/8 thread). Might balance better with any but EL bodies (I only tried it with 553 ELX, so camera is quite a bit heavier, contributing to end heaviness), so I'll stick on 503CW to compare.
BTWm, love the lens, the long throw focus with astonishing precision (there is a 60 m mark before infinity), so separation looks super sweet.