[JasonACT]

Well, it erased ok, programmed ok, verified ok... But in diags mode I only got back the FGX VIN though???!!!
Checked my program, I had forgotten to switch over 2 references to my data, I had only done 1. So still pointing to the FGX.
Attempt 2... erase fail. WHAT?! I had put back exactly what was where, how could it possibly know to "protect it" due to a discovered hacking attempt?
Reset my Arduino, reset the IPC and try again...
Erase ok, write ok, verify ok... Diags now show my VIN in the unit, but since this is the FGX cluster with a different firmware, I'm not putting it in my car to test!

I'll need to do all this again now on the spare FG2 unit I have, and before that, consider a better way to get access to pins FLMD0, RXDA0 & TXDA0 (RESET I don't need, a power cycle can do that).

Interesting though, the FG2 unit is from a ute, it has a lot of differences to my data in that sector. The FGX one has a new firmware, but only a single byte difference (0x01 vs 0x02 a quarter in) in this data. So for all I know, the FGX may work in my car.