Another coat of paint has definitely made a big difference to the side
of the truck. It really does take a few coats to build up the opacity.
And I got one tab welded onto the air pipe, and as expected that was
the last dregs of the argon.
Thankfully, I got my brother to grab a replacement bottle, so that's sorted. I've done nothing directly to the truck since those pics (from the 8th), but having gotten more argon I did give TIG brazing a try on the aluminium and it does work a lot nicer than doing it with gas; probably because of the more concentrated heat.
But it makes it incredibly obvious just how important the flux is to it even being possible to work with. As long as there's flux there, it makes a lovely join just like tig welding; but as soon as you get to a point where there's not enough flux, it just suddenly stops flowing and just becomes a big ugly blob.
So I've bit the bullet and bought a new welder, that does AC as well. It's another magic mystery brand-of-the-week china made one, but I've had pretty decent luck with that so far. (Frustrations with the torch on my mig welder aside, anyway!) We'll see how that goes; I'm quite excited. Having the capacity to do aluminium is something I've missed since I left the bodybuilding shop...
It's been a while since I've welded aluminium, but it's going quite nicely as I get the hang of it again.
I think it's going to work out. Maybe. I have to be careful about the amount of space I have left, but I think I can make it work. (And if I can't, I guess I get more welding practise? The nice thing is, the component parts -- flanges and whatnot -- are pretty simple items to make, without needing to have somewhere laser-cut them for me; so if it turns out that it just won't work, I can make new ones and take a different tack. Though I would have to order more injector bungs.)
After all, it's got to fit underneath that engine cover. 
The engine
cover is now also bolted down where it should be, through the proper
holes; though it does appear I need to extend the hinges slightly to
capture both bolts on each side rather than just the uppermost. It'll
do for now.
In the process of doing that, however, I've discovered a broken spot-weld that's supposed to be holding down the rear panel of the engine-hump, and which has allowed everything to slump backwards to the extend that the cover no longer latches properly; so I'll have to do something about that before too long. No big deal, but it will mean a little more damage to the paint I thought I was done with.
Still nice to fill up some of the gaping hole in the cab, mind. Makes it feel a bit more finished, just for a moment.
At some point next week, I've probably got to find myself a piece of
heavy plate I can use to make a jig for manifold welding, try prevent
it turning into a pretzel that won't seal. (And if I use my brain, I
can make it match all the ports and bolt-holes on the head... Not that
I foresee there being a great demand for manifolds for a Bedford 300,
mind!
But it would help with perhaps sorting out that slightly wonky front manifold that pulls up a bit funny and tends to blow the gasket out...)
Anyway, that's a lot of words all to say that the new welder is
working out nicely, and I've spent several hours making horrible loud
buzzing noises and melting aluminium.