Many years ago I had a 38 Plymouth. Was thinking to convert to 12v setup, to prep for an eventual V* conversion. had a long talk with a local starter shop of good repute and was told that it that the starter would run fine with 12v as long as the engine was easy to start, as in it didn't take a bunch of cranking to start it. But if I want to they could rebuild the starter and upgrade it to 12v operation when/if it failed.

I had an old timer sit down with me and we discussed the other aspects of swapping over to 12v operation and his comments on the gauges pretty much mirrors dogdays statements. Since it had no wipers that wasn't an issue either.