Lightened my wallet for some exhaust wadding; but it'll be a couple of
weeks before I have enough in reserve to buy the material for skinning
the silencer. Still 50/50 on whether I want to wait and try it without
the wadding first! 
In other items, I have gotten a pressure limiting valve ordered so I can try get the brake response under control, and my boss has donated an air-tank to the project so I can have a 3rd circuit to run additional gubbins like air tools from.
...Okay, he didn't intend to donate it, but after a hasty git-'er-done bodge a few months ago where the trailer's levelling valve was hastily welded to the end of the tank after it fell off its previous mount, the tank had to be replaced due to stress-cracking. (Turns out, waggling a levelling valve around on the end of an 8" lever arm is quite a bit of force to put on a piece of 3mm plate!)
So I had to replace the tank on the trailer, and I kept looking at the tank I'd just removed -- which wasn't that old, 3 or 4 years or so? -- and thinking "I think I know exactly where that'll fit on my truck"
Cut the mounting bracket off the end of the tank, cleaned it all back to bare steel, welded up the stress-cracks, then patched over the lot of it just for a bit of insurance. Should be good!
And I was right, it fits in here absolutely perfectly! Need to make up some mounting brackets, and sort out fittings, but I think that's going to be just grand.
... do I really need a separate tank to run tools n stuff off?
(Especially since I don't think this is much -- if any -- bigger than
the main tank already is.) Not really, no. I currently have a
quick-fitting attached to the manifold for the main tank, and that's
been perfectly sufficient for everything I've used so far; but,
y'know... free tank 
Plus, it would be nice to have quick-fittings in more convenient locations that don't require me to crawl under the truck to connect my air-line.
