It's unlikely you'll be able to swap tumblers. If the slot pattern on the aftermarket switch is the same as the GM key, have a locksmith re-key it so the GM key will work in both the doors and the ignition.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!