My last purchase was a metre long piece of M8 threaded stud, which finally seems to give something like the counterweight or leverage required for a conventional post and gimbal type design. What seems to be needed now, is to get the centre of gravity of the camera directly above the post that goes down through the gimbal. I've also discovered that the tripod mounting hole on my Sony PC110E DV camera is way over to one side; nothing like the camera's centre of gravity and that's even before adding any lense adaptors or weightier batteries.
Ideally the rig should have some fine adjustment threads to allow the camera to be positioned accurately on the top-plate.
There are a few more refinements to make before this is worth trialling in any way, the next couple of things to tackle are...
1) The rather awkward length of the post could be reduced so long as I can find a decent way of adding some counterweighting instead.
2) The tube that forms the handle needs to be extended to make it easier to hold the whole device up.
I'll post some more of this if/when it gets any better.