Looks promising.
Not my prettiest weld, by a long shot. But it's in, solid, and there are no big leaks. I still need to go over it with some soapy water and see if there's any pinholes, but I need to come back at it with the torch at some point anyway for some other mounting points so I can deal with that then.
And it'll go like so!
Second one turned out a lot nicer as I get things dialed in. Still not a pretty weld, but it's not too hard to tidy it up, being nice soft aluminium.
Two down, one to go. But it was getting pretty late in the evening, at that point (Past 9pm); so I decided to call it a night, as it takes about an hour to do each one.
Process is pretty simple: drill a hole on the wonk (approximately 35 degrees), open it out with the burr and fettle until the injector bung sits just nice, gas weld it in, clean up all the flux and knobbly bits of excess aluminium, and it's good. (ish.)
I still need to trim the excess of the injector bung where it sticks into the manifold, and make sure that's all nice; but that can be done at a later date. As mentioned, I still have additional mounting points that need to go on and whatnot; but I have to see where all of that lands, before I start making them permanent.
I have a plan: it's a dynamically adjustable adaptive plan using
flexible reactive feedback mechanisms. (Namely, I have a rough idea of
where I'm going, but I'm otherwise making it up as I go along. 
)