The coil could have been the source of sudden failure and some have been known to do just that when hot only to work again when cold. Reversing the polarity would not have done it by itself--the coil will work either way.
The thing about the coil polarity is efficiency is not as good when hooked up backwards because the spark wants to jump from the shell to the center electrode instead of the other way. With the shell always being cooler, and sparks more efficient when generated from a hot surface, in the case of marginal plugs or other problems the spark would not be as powerful if backwards and there could be misfires or a hard start.
Assuming you have the original coil then dist would be pos and bat would be negative terminal on yours. You could reverse if you wanted the battery the other way.
If you want to check yours, here is a link to a way.
http://mgaguru.com/mgtech/ignition/ig104.htm If you do use the pencil method, remember graphite is a decent conductor so stay on the wood or you might get a jolt.
One further note: with the ign switch problem you found, that would also be an excellent source for the sudden quit.
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