Take the hub off the axle tube and look inside it with a bright flashlight and an inspection mirror. You should see the outer bearing races (the cups) seated firmly against the bottom of their counterbores. If both cups are in all the way, one of the counterbores (probaby the outer) will need to be machined a bit deeper to allow both locknuts to get a good engagement on the axle tube. That shouldn't be a big challenge to a machinist with an accurate lathe and a 4-jaw chuck. Hopefully, you'll find one or both cups aren't seated fully and machining won't be necessary.
Jerry

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