I need to mount a tripod head on a bit of scaffolding. The intention is to use this on that dolly of which I've occasionally posted images, which has an upper frame made out of 2" alloy tube. The current approach is to put a tripod on the floor, which is rickety and unstable and severely limits minimum lens height. With a scaffold adaptor to mount the tripod head, things would be sturdier, and custom arrangements become possible.
The tripod head most likely to be used has a 75mm ball, but I'd rather design for 100mm on the basis that adaptors exist and future-proofing is good.
If it's just a ball receiver of the type used to make a hi-hat, that's fine, as I can fabricate a simple intermediate plate with conventional scaffold clamps.
Obviously, there are many ways to do this. As this is largely giveaway gear on which I will never make money, it's important that the solution is cheap. I'm after something that will work on the occasional job, not something that will go out week in week out on a rental basis.
Essentially, I suspect, I'm asking for sources for a very cheap 100mm mount of almost any sort that I could adapt to what I want to achieve. Any ideas?