A bike came in with all original parts, including seriously corroded and stuck index shiufters that could not be brought back with all the lube in the world.
So what to do?
Apply pure friction shifters. Sure, they're cheaper than almost anything, but they're mostly metal, plenty durable, and VOILA! You'll never have parts compatibility issues again.
Result: One really easy-to-shift bike that's a hoot to ride.
(Friction thumb shifters can be found through most bike shops for less than $20 a pair.)
A little drop of oil dribbled into the friction points of each shifter, and another added to the cable head before pulling inside the recess of the shifter lever, will help everything run smoothly.
Pro tip: I like to add a wrap of cloth handlebar tape under each shifter clamp to give it better purchase on the handlebar. (And if you work on your own bike, keep a roll or two of cloth handlebar tape handy for this and other quick fixes.)
Have fun and happy riding.