Paul - If I turn the clamps round so the bolts face downwards the ends would be about 1/2" closer to the ground, while if I try to turn them so the bolts are parallel with the ground they'll foul the chassis rail. Where they are at the moment and with the suspension set up I have settled on (excuse the pun) they have just enough clearance so I'm happy with them.
Scottie - I addressed the front tyre clearance issue by moving the whole bulkhead back 20mm on the chassis. That was simple enough with the body off, I just drilled new mounting holes 20mm ahead of the originals and bolted it on.
Even then I still had to 'adjust' the clearance by bashing the front faces of the bulkhead in with a lump hammer - you can see the slightly concave effect achieved in the picture below. That worked but now I've switched to 80 profile tyres from 70's the tyres are
just skimming the paint off the bulkhead whilst manoeuvring.
This isn't a problem on the road but I'll have to sort it before the next MOT. Similar to your suggestion I'm thinking along the lines of cutting an 'H' shaped pattern of slots, pushing the resultant square sections inwards and welding fillets in to restore the integrity of the bulkhead. On the plus side, at least the tyres are marking the exact points where the modification is needed.
The good thing about this low budget rebody thing is, as Yoda would say, 'Impossible is nothing.'