So.
The key things to know are the sizes of the screw threads - which bizarrely are metric M10 x 1.25 at the pinion end with banjo bolts, and then at the other end with the tightly-radiused pipe and a union compression fitting with a small olive, they are 7/16ths UNF - so those are the fittings needed if it is possible to get 90 degree banjos for the 7/16th UNF end as well it would facilitate things, but those are apparently unavailable (at least with the supplier he is using?). I believe though that I have identified UNF fittings that would work used on Harley Davidsons, but these are reasonably niche, and the prices are surprisingly strong for quite small parts.
I never really got a clear answer of why it wouldn't be possible to do this with solid pipe but that - to my reasonably mortal shame - is because I was having real difficulties understanding him ; I've lived up here over 20 years and normally am reasonably able to understand and communicate but not on this occasion.
The pipework from end to end is 4mm hydraulic pipe with a flexible steel mesh outer. It would fit under the heat shield plate. It is rated to 2000psi, but I'm still havering on whether this is a viable solution. Plus - in non-stainless with VAT it has cost me just over £100 as a garage spare part - viable as a backup perhaps. He reckoned stainless would be around 140+VAT.
Put it this way. I believe it would hold fluid and transfer it better than a corroded out original pipe, but is what I have in my garage the perfect solution?