It's possible, and relatively simple give the skill and kit, to skim the difference between the cassette widths from the back of an 11 speed road cassette on a lathe. I've done it a couple of times, and it only took about 5 minutes.
Obviously depends on having access to a lathe or someone with...
Re:
I've a load of Michelin DH tyres, comp 16 2.5"&2.2&, comp 24 25."&2.2", mud 3 and a trimmed mud 2.
Also got an E13 bashguard, and a few parts from an original MRP chainguide.
Pretty sure I've a goldtec DH chainring knocking about too.
Re: Campag 10 speed shifters.
I should have a set of centaur brifters going spare next week if they're any use? Swapping my commuter bike to 1x10 shimano so once I've found the time to sort it....
The shift down lever on the left side occasionally catches on the brake lever but otherwise fine.