Strange thing Google groups not allowing me to enter a follow up.
I have gone a stage further with my efforts. I started off with a180mm by 46mm steel disk and used a mill to produce a 25.4 mm square grove around the diameter.
So as such the inside diameter is around 130mm, side walls at around10mm.
I gave this a try on the home made hydraulic bender I have made with very poor results.
The bend started well with the top surface beginning to sink in, the side of the square tube being well supported by the 10mm walls. Then at some point the tube just lifted from the die and the whole bend happened at one point. A crack appeared in the metal as it ripped it apart. Si I guess that a 2.5 D radios is too tight for this set up.
The guide rollers could be a bit far from the centre die, but think the same would result even if closer.
So next step is to try and make a bender along the Hilmor or other ideas and use the jig I started to build as some form of press. I only used a small 2 tonne bottle Jack but it was capable of bending the tube.
One lives and learns hopefully