I'm not sure when the switch to negative ground took place, but a quick check of the wiring diagrams in my Haynes manual doesn't show negative ground until the Mark III Midget/Mark IV Sprite. In any case, if you car is running negative ground, presumably it's been converted. If the car has been run that way, it's obviously OK. So, it's water over the dam at this point. Sounds like your concern is that it never was converted but that maybe some lemuel hooked it up negative ground and left it that way.
As for negative-ground conversions--the regulator, generator, starter and so on won't be affected. Yes, it's best to repolarize the generator when you switch from positive to negative ground, but it's likely that you won't notice it if you don't. The current leaking into the field coils from the ignition idiot light will probably be enough to get the generator started right, and once it's running with the proper output polarity, it will magnetize itself in that polarity. Just to be safe, you might want to do the polarization. It's easy.
An electronic tachometer won't work if it were set up for positive ground, but there's an even chance you wouldn't have blown anything. The fuel gauge should be OK. I'm not sure about the wiper motor--if it has a field coil, it won't matter; if it doesn't, it will run backward but that might not matter. It's a good idea to reverse the coil primary leads when converting, which might or might not have been done, but the car probably will run OK even if this is neglected.
Thre's probably something else I haven't thought of--but all in all I don't think you have much to worry about.