OK here's a useful resource:
With a linked sheet of all results that people have entered.
Despite the thread I originally found, no one has got that particular RAM to work on the sheet. There's another Crucial item:
CCT16G4SFD824A
Which has 10 reports of working in the 224+
Return initiated, new RAM arriving tomorrow. £10 more expensive so £35.
<edit> New RAM in and booted fine. Takes a little longer to come up (I assume it takes a bit longer to check 18G of RAM than 2G 🙂 I think I'll start another thread about how I'm going to do this.
C