This morning I realised I had the RAM incorrectly placed (you need matched sticks in both banks, but from inner slots to outer), I'm now reliably getting a boot chime but after about five seconds the red "checkstop" LCD turns on and the machine switches off. Now it's time to pull the LCS and CPUs; from what I've read even if the LCS looks OK the coolant may have evaporated out slowly and/or around the CPU block that I currently can't see. Still, some progress.

JB