I respect your commitment, but I'm just going to swallow it and try to make the best of it.
As of this morning, I have a glimmer of hope.
I stripped most of the bodywork off, taking photos along the way and noting all the various things that needed doing.
The ABS is completely bypassed and the steel lines, those that remain, have been bent in odd ways and places. The ABS block itself though is sealed at all ports so there's hope it may be restorable.
There was no oil in the sight glass. It took at least a half litre to bring it up. No sign of mayonnaise under the filler cap.
I dumped the mayo out of the overflow bottle and cleaned it out. Thoroughly degreased it inside. It came up pretty good.
Checking the radiator cap in good light there is coolant, just not up where it should be.
Started it up, sounded like vintage tractors having hate sex same as before and it puked a TONNE of smoke. The wife even came out and complained about it being sucked into the house. It eventually stopped after five minutes or so. Put the balancer on it (Twinmax, so I do two at a time, referenced to the one directly connected to the throttle cable) and balanced the throttle bodies (big brass screws). They were badly out. It now sounds like an actual 4cyl engine with a steady idle at a bit over 1000rpm. I checked the vacuum balance at 3000rpm and the two TBs I checked were slightly out but the throttle plate screws appear to have been Locktite'd and I don't want to risk breaking the screw heads so that will have to wait.
Let it run right up to temperature and the fan activated properly, so that's something. Nothing pushed out to the overflow tank though, it stayed cold throughout. I opened the cap under the tank and the coolant has come up. Cleaned the bottom of the cap, confirmed it does allow the system to suck water back in, topped up the radiator and sealed it back up. If that doesn't pull coolant back up the hose the I have a leak somewhere. No visible coolant leaks around the radiator or pump *that I could find*.
Did not notice any "fizzing" in the coolant with the engine running and radiator cap off, so the head gasket may be ok after all.
Admin, if you want to move everything past where I started finding problems to a new thread in something like a blog section that wouldn't be inappropriate at this stage. Then I could post pictures as well.