Nick, in this case, it was pretty easy. Once I found out that they were track powered, I just had to locate the resistor and install the correct value. As I said, the hardest part is getting to the resistor, you have to be careful with the little 1.5mm connectors, the wires are small and break easily if you yank on them. For the powered unit, I'm glad I now know the wiring is really out of the way of the flywheel, that's certainly killed a lot of these. That was the only red flag I saw looking inside.
Some thought was put into the lighting mechanical design on these, most of the lights are on the one board. I suspect that makes it easier to build and test.
It is interesting that one resistor was too low in value, and the other resistor was too high in value. There was a 22:1 difference in light output for the number boards between the two units!
There's an old saying about the right hand knowing what the left hand is doing... 
I'm happy with the final outcome, they look like they belong together now.
