Not much progress made, recently. I've been wrapped up in a body-building project at work that has been sapping my energy. (Also, it's getting cold this time of year!)
I do have a week off coming up, and though I'm not making any promises about progress, I'd like to get some stuff done.
But, anyway...
And that goes in the mystery extra dipstick hole on the side of the
block.
I also checked the silicone reducer coupling fitted the throttle body,
and it does. So that's good! Pity it's bright blue, but I'll not see
it when the engine cover's closed, so I can live with that.
Spent some time fixing the pedal on my TIG welder, which turned out to be the most comically flimsy design. The 'pushrod' from the pedal down to the potentiometer is a flat piece of 0.8mm steel, and the switch that tells the welder to start welding is a microswitch with its little roller running on the thin edge of that 'pushrod'; so once that thin steel bent a little, the microswitch roller just kept running off the side of it and springing out enough to turn the welder off. Brutality occurred, and now it's fixed.
Which meant I could then do a little more work on the air filter
housing. Mostly just extending the outer edge of the casing, so that
the filter now fits within it; but I did also go in and smooth out the
seam down the side. Unfortunately can't do much with the seams at the
bottom, because they're quite difficult to get to from the inside.
Next step for the air filter housing is the outlet to the engine, which is a bellmouthed tube that will protrude into the centre of the filter.
Sort of like that, yeah. 
And then I'll have to figure out the exact details of how I'm mounting the housing and where, make up the mounting points for it, figure out where I want the air inlet to be, and all that sort of stuff. I'd like the air-filter to be easily accessible from underneath the front of the truck, but drawing air from higher up. Oh, and I've got to come up with some method of retaining the lid, too.
The good news is, I've sold the bike (which was mouldering around the side of the house for the last few years), and that's put a few more pennies into the pot. (Naturally, the bloody thing refused to start and stay running when he came to pick it up, which I think was largely that the battery's not liked the colder weather of the last few days even despite me having it on charge previously; so I didn't get quite as much as I wanted, but still, it's better than nothing.)