Next step is to increase the wall thickness of the swivel bracket by soft soldering a piece of the small tube inside it.

I use additional solder flux - see the pictures, it may look German but it's made in the UK. this helps the solder to 'bite' and flow - basically the solder will only go where there's flux. Brass in particular needs lots of it. As my jewellery teacher says "flux is your friend".

After soldering the centre is again cut out and filed to accept the swivel screw. I've used a piece of 0.8mm stainless steel wire as the pivot, locked in by coating it in flux and re-heating the assembly with a soldering iron. The solder just runs enough to lock the pin in. All that's left is to drill 2 bolt fixing holes, and reduce the height a bit until it looks right.
I find it easier to make things a bit big, and file them smaller, than the other way