Welcome to the group, and the wonderful world of antique bikes!
If you're using starter fluid (which is really hard on a motorcycle engine) and you know you have spark, then you should have fire in the hole.
The only thing that would get screwed up by reverse polarity (at low amperage, like a battery charger) would be the ignition module. If you have spark, then it's probably okay.
The fuel pump only runs when the engine is running, so that might be okay too.
It's hard to know what may be damaged if you don't know what was working before this happened.
Let us know what you find out!
Currently Running Stable:
2010 Honda NT700V
1986 Shadow 700
1986 Honda Trail 110 (Postie Bike)
1987 Honda Rebel 450
1973 Honda Mini Trail 50