Hi Steve,
As BDA says, technically there isn't a problem and I'm sure you'd get past an MoT with it.
The snag, drawback, risk, however you want to phrase it, is that you're replacing a long length of metal pipe with a flexible, non metallic tubing. The stainless braided lines do tend to be better in terms of pressure flexing than conventional rubber lines, but they do move. The general principle that most folks follow is that to improve the brake pedal feel (get it as hard as you can) is that the first thing they do is minimise the size of flexible lines, then you replace what you've got left with stainless braided lines.
Will you notice it in practice ? Like BDA, I doubt it because the rear drum brakes don't do a lot in terms of stopping the car.
Would I do it ? No, I don't think I would. Rally cars and race cars get a lot of maintenance and the lines such as you've shown are probably checked visually every race. The line along a radius arm might get checked once every year if it's lucky ! The length along the radius arm is a very simple run of pipe and very easy to make, probably one of the easiest bits on the car so I would replace both sides with metal.
It's fit and forget if you use Kunifer (Cunifer alt. spelling) and if you do the front flexibles at the same time it'll be done for years.
Brian
