The loss of the cages is meaningless. If the races are OK, rebuild with loose balls of the same size.
Switching to Sq. taper means buying an adapter (if you can find one), new BB, and new cranks. It would lose any character of being what it is, and odds are a suitable frame with OK BB and cranks would cost less anyway.
Your call, and hopefully JT can point you to a source if you want to go the new cranks route.
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