h'Okay, then! With the engine fitted into the truck, and now with all the mounting bolts tightened (Other than the front ones, anyway.), I decided to stick the various manifold bits on just for a laugh.
They fit better than I expected! Now, admittedly, my expectations were "not at all", what with me having forgotten about the existence of the front axle while building them, so there's that...
Looks pretty good, eh?
...except it doesn't bolt up to the head, because the bottom of it is hard against the top of the diff casing. But the good news is the front half bolts up lovely!
...aaaand it points directly at the front of the diff cover. 
Oil warming, y'see.
Now, I knew the inlet manifold stubs were too long, but it's easier to
leave them long and cut them down to the right size when I know what
that is. There's no massive rush on the inlet manifold, anyway; I can
use the carbie one to run the engine for the time bean.
I've also hooked up the various electrical plugs and the power & ground leads, and can crank the engine over from the button on the dash. My warning lights for oil and alternator aren't working yet, and that'll be next on the list as far as electricals go. (Alt warning I'm about 99% certain I know why it's not working, and that's because the wire's been cut because I needed to extend it and never reconnected it to the bulb. Oil warning light, I'm not so sure about.)
So the immediate priorities list is:
- Front engine mount
- Warning lights
- Rework the exhaust manifolds so they fit!
- Fit the clutch
- Finish up & fit the gearbox
- Throttle cable
- Radiator
And that should put me in a good place as far as allowing me to carefully drive the truck forward & at least partially out of the unit so that I can get to the lockers on the O/S! ...I really want to get the compressor out, in particular. (Also, I'll probably find the wiper arms that I got last time.)