Without a finder scope attached to the top tube, and using the biggest EP I currently have (30mm 1.25" Vixen NPL), the top tube is approximately 2.1kg. The bottom tube with mirror is approximately 4.7kg.

Using Robert Royce's truss length calculation spreadsheet, this gives me a separation between the bottom and center tube of only 120mm, about 4.75". That's "not enough" I don't think for it to be aesthetically pleasing. By making the top tube heavier, I can move the balance point up the scope to increase the separation between bottom tube and middle tube. The photo I took in the last entry had a gap of about 12 inches which is a bit closer to what I was expecting.

It would be nice if the scope was comprised of two sections of roughly the same height, so they would stand side by side, perhaps in a lightweight crate or something. This happens at roughly 11" of separation between the bottom and middle tubes and in order to get the balance point to the middle of the center tube at this separation, I need to increase the weight of the top tube from 2.1kg to 3.3kg (maintaining it's own center of balance).

There's four thoughts in my mind at the moment:

1 - go large with a finder on the top tube

2 - add a sliding weight underneath the top tube.

3 - add a heavier weight on the center tube, somewhere forward of the altitude axis.

4 - mount the altitude bearings further back than the center of the center tube.

I may go for a combination of the above. On one hand, I think I'm being daft by ignoring the scope's own center of balance, choosing style over substance if you like - especially when this comes at the price of actually adding weight to it. I think, truss rods included, I'm going to come in at 10-11kg, plus cradle and some additional fiddling. On the other hand, I can choose the look of the scope to be right in my eyes and then make good. I've made the rest of it up as I've been going along, so I'm not too worried.