Just a quick update, the MLT power supply is fitted and the set is alive again.
On the Phiphong PSU there is a 4 way cable (2 x ground & 2 x VADJ) - this cable caused me some confusion as I thought it was the 16v line, but looking at the main board in detail shows this is actually a 12v line - ran 12v from the MLT and "job's a goodun"
I've got it on burn in test now, looping some high bit rate MKV files to give the main board a good workout.
Thanks for all your help, with particular thanks to CDEL for pointing me in the direction of the MLT psi.