We reversed the + - battery cables by mistake and cranked it. Then discovered what was going on and reversed it. Any possible damage we might have done?
Probably not. Put them back on where they belong and start it. If it charges and your ammeter is correct, you didn't hurt nuttin.
Death on a electronic voltage regulator.
Older engines that didn't use any of the newer transistorized, electronic devices in the electrical circuit are pretty forgiving when things get reversed or shorted. That doesn't mean it can't happen. It just not very often.
If a Fun Projects Voltage Regulator was installed you likely destroyed it. Sometimes they can survive but then turning the battery around if it is damaged will then finish it off. Contact me BEFORE you try again with the battery polarity corrected if in fact you had a Voltage Regulator installed on the car. Please don't proceed to just "try it" first.
Crazy as it may sound, I "highlight" my battery posts with the "+" and "-" with one of those yellow paint pens. Often it's kinda dark "down there" working on batteries, this helps to see what type post better, not to mention to "wake ya up" when you're doing it.
Oops, I apologize for giving misinformation. I did the same thing once on my '38 Ford and didn't have a problem but that didn't have any modern electronics to deal with. I hope it works out okay.