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Will they fit? In a word, yes. Is it worth the time, effort, and cost? No. If that's the route you want to go, you're much better off just finding a 4v motor to swap in.
They'll physically fit, but it's a lot easier to get the whole motor. There's a laundry list of little parts you'll need to make it work. Honestly, I wouldn't bother.
And this is coming from someone who actually did it.