[jlawler]

The engine just dies. Not spluttering like a fuel issue. Just dead coasting down the road at 60mph engine being turned over by the vehicle. Rev counter drops to zero.
Feels much more like an electrical/ignition issue than fuel in that it is sudden death (though I know the relay also feeds into the injection system).

I double-checked the fuel pump relay seating.

Thanks I'll try the MAF test.

I'm suspicious because of the previous problems that it related to fixing those.
Hence the Temperature sensor could have been damaged during getting the head reconditioned. It took me a while to track down the previous CPS sensor issue so I would have been messing around with the ignition relay, ignition amplifier etc.
Though I did re-heatsink that at the time.