I'm considering buying a '74 sportster with a right-side shifter. I've been riding since my elementary years and am concerned that in a time of crisis I'll revert to old habits and will hit the wrong side. Am I overthinking this??? Thanks.

 

It will take some time to be comfortable riding with the R/H shifter and yes in a time of crises you will revert to old habits.
I had a Bultaco persang that was a R/H shifter, been riding Japanese dirt bikes all the time before this bike, and in several occasions I need to hit the brake and ended up down shifting, didn't get hurt but it scared the S%&T out of me.

It will just take some time and riding to become accustomed to riding with a R/H shifter.

Hope this helped.