Update
I thought I'd check some basics today.
As said, when I drove her off the truck she was misfiring like mad and emissions light flashing.
After a long charge of the battery I investigated further today. Codes were for misfire on cyl 1.
Removed 1-3-5 cool pack. Plug well 1 was full of water. All boots on the coil pack badly split.
I dried out the plug wells and checked the plugs. All black nasty and sooty but not wet. Refitted plugs and a good spare coil pack.
Now runs on all 6 with no misfire

I did a compression test after this to get a feel for engine health.
Pots 2-4-6 were all bang on 225psi
Pots 1-3-5 were all bang on 200psi
Although not a massive drop it set me thinking. So I checked Cambelt setup.
The 1-3-5 bank was an entire tooth too retarded.
I set up the cam timing correctly, the 1-3-5 pots are all now also 225psi

I have not been told the engine has cooked (due to oil and water mixing).
Based on the above I'm thinking I might leave the heads in place, just change the cooler, and do many coolant flushes to get rid of the nasty brown goo....
Thoughts?
I will do the stat and hbv whilst accessible. And the Cambelt kit. And full service etc once back together.
I also found a hole in the servo main vacuum pipe. Quite a substantial one. Could this be introducing unmetered air and account for all the plugs (incl 2-4-6) being dry and black?