Since I won't need my donor unit any time soon (older model year than my current '40) I decided to rip it apart for the greater good and for my own amusement.
I think I have good news for you: there is NO 'intelligence' whatsoever in the driver-facing half of the gauge cluster!
That supports my 'you only need to swap the PCB
' theory, making the KM/h-to-MP/h thing a very doable modification.
Remove the cluster back cover (6 + 4 screws), then the 8 phillips screws that connect the board to the plastic body and those 3 flat cables, that's all!
An illustrated story of my findings:
The white plastic frame that holds the gauge part of the cluster together is connected to the faux-wood fascia by seven (3 horizontal rows: 2-3-2) small phillips screws. The LCD also connects to the fascia panel (2 phillips screws) and links to the front side flexible board for signal input and backlighting (see further down).
The warning lights, dash illumination and gauges are all connected to one flexible board, seen on the picture below. This flexible board gets it juice & inputs through the three flat cable connectors on the main PCB.
This flexible board has soldered clips (3 each) for the gauges that both supply gauge signal AND keep the gauges into place physically.
I removed the board by gently undoing those connectors/clips one by one, with this as result:
With the fascia and board disconnected I could isolate the gauge units from the cluster, and 'prove' that there are no electronics there beyond the gauges themselves...
And a shot from the front: you can see the separate gauge units with the fascia removed:
Hope this helps,