The car is starved for attention, and decided to get some in a potentially dramatic way, with a fairly sudden hot low oil pressure problem.
So I went and changed the oil & filter -- no glitter at all (hmm) -- in case it was just degraded. That didn't fix it. So I order bearings, and go to park the car up until I can tear the sump off and investigate. When I park it up, I notice my alignment has gone all to hell and one of my front tyres is shouldered off down to cords. So I go to check and adjust that, and in the process discover that the front spring on that side has snapped.
Also in the process of adjusting the tracking, I managed to ding the threads on the track rod end and get the nut stuck.
Track rod end and spring get. Change the track rod end, drive the car up closer to the unit to do the spring, notice that the oil pressure switch is wet on the connector end.
Like, almost dripping levels of wet. Joining some dots (the oil on the end of the switch; the neat effect that turning the engine off for 30 seconds while the oil pressure warning's screaming, lets it run for another minute or so after restarting before the warning starts to chirp again; and that there's not a single sign of metallic flake in the oil, even on the pre filter side of the oil gallery, behind the oil cooler feed port plug (oh yeah, I also found out that an oil cooler was an optional extra on that engine)) I think the switch has just started to go bad.
New oil pressure switch is on its way...
Anywho!
Compressor outlet line running to the hard feed, and there's a matching one for the other end of the hard-line to the air drier that I'm waiting on fittings for. Stainless braided hose rated up to 20bar; that'll be more than sufficient!
Next little jigsaw piece was the purge tank for the air dryer; used for what's termed "regeneration", it holds air that's then dumped back through the filter to the dryer unit's exhaust once the relief valve satisfies and the unloader is tripped, blowing accumulated moisture out of the exhaust. Gives a longer useful life for the dessicant cartridge.
It's a little on the big side, a 10 litre tank from a Mercedes bus
that was headed for scrap after a fire. But, waste not, want not! 
A little more plumbing, and that portion is ticked off. I have fittings in the post for putting the other braided line between the branch of the T-piece in the background, and the open port in the dryer unit in the foreground. (And the little elbow fitting to connect the air-line to the unloader valve, and ...)
Still more parts needed, but I am drawing closer to the point where I can build air pressure in the system. I did notice, though, that the edge of the compressor belt is just grazing the crank trigger wheel, so I might need a bit of a spacer washer to move the pulley slightly further out for clearance.