Welcome back:
Honestly, anything is possible, but before I go to that extent (key lock assembly) I would check the other things to confirm it isn't something simple. However, if he said that the switch is the problem, my guess is no matter what is wrong, he will tell you the key needs replaced. Plus, the key wasn't an issue prior to the new engine, so why now? I could better understand a fuel leak or injector leak dropping pressure before I would think the switch suddenly went bad.
Let me know what you find. Also, if the ignition switch engages the starter, everything else is getting power, too. Thus, I doubt it is the switch. Not being there makes it difficult for me. I hope you understand.
Take care and let me know what you find.
Joe
Tuesday, March 26th, 2019 AT 5:15 PM