So countersunk screws - sometimes the solution stares you right in the face ...
After fruitlessly messing around with the bracket that came with the V8 exhaust, it became clear that it will be simpler to make a new one.
So made a cardboard one to see if tc1cat's tip would give enough clearance.
And as you can see, it works!
Just need to get them a bit lower and a bit farther out from the frame.
The bracket will be held on with 3 M2 bolts. Should be sturdy enough if I use the 0.5 mm brass plate I have sitting around.
I can gain some more air if I grind of a mm or two of the bottom air tank. This would be invisible from the side as it is covered by fender.
The bracket will be practically invisible from the top too.
Roughly will end up looking like this. Will elongate the holes for the bolts for adjustments.
Using a countersunk head screw for the fuel tank support also solves the problem of the head interfering with the gearbox/motor support bracket.