After looking at the problem from all angles, I decided that the only way the pipe would fit was if the bracket was removed and either relocated or a new bracket fabricated and welded to the pipe. So I apprehensively fired up the angle grinder with slitting disc attached and cut through the 5 welds holding the bracket to the pipe, thankfully without doing too much collateral damage to the pipe. Once free of the bracket, the pipe wrapped round the block without fouling anything and could be manoeuvred to a suitable position without any effort. There's enough slack in the flange mounting holes to give quite a range of adjustment, as it happens.
It quickly became apparent that the existing bracket would not be able to be re-purposed and that a new bracket would have to be fabricated and welded on. Time to break out the cardboard and make a CAD template. What was also rather alarming was the degree of corrosion that existed between the pipe and bracket. Being only tack-welded in place, and not sealed off, corrosion can (and does) form between the two skins. At least I'll be able to arrest that particular piece of rot while figuring out a way of making it fit to the multi-purpose bracket.
In other news, the A4 stainless M10 x 1.0 drain plugs arrived and one of them was fitted to the block, using generous amounts of Wurth CU800 anti-seize paste. It's a taper thread and screwed in leaving about 2 mm of the total 10 mm depth proud of the block. I'm cautiously hopeful that it should be a long term solution.
