I cannot find anything on an on-board metric-SAE or SAE-metric converter on board the Hummer. The signal for the speedometer and all speed related calculations are picked up of of the Speed Sensor which is on the transmison.
The gauges would have to be converted. You would have to change the sender and the gauges. Then there would be the issue if the computer would have any problem with it. That is something that an importer/exporter might know. Look around for japanese Domstic Market parts and see if somone working there might know if the Computer would be okay. I would think it should be if you change the sender and gauges as the gears in the transmission are the same. But, that is the kind of information that is not readliy at hand.

If it helps, the conversion for kilometers to miles is=Kilometers * 1.632172=miles.

I will look elsewhere if you can tell me where you heard of the conversion procedure.

Answered by DrCranknWrench (expert)
3,292 answers provided

The odometer cannot be toggled between km and miles. It requires a different IPC and BCM configuration.

Answered by factoryjack (expert)
4,285 answers provided