Sh66: Use the map. 
The letters you've got are correct, at least the ones needed for the solution.
The missing 'c' is likely a typo.
What "is shown" - well, what's shown there, what's shown in the whole level?
The comment in source - maybe it was added since the uranium is referred to like it were harmless, but it might be a subtle hint for another level, where it indeed can harm you. ¯\_(ツ)_/¯

The letters you've got are correct, at least the ones needed for the solution.
The missing 'c' is likely a typo.
What "is shown" - well, what's shown there, what's shown in the whole level?
The comment in source - maybe it was added since the uranium is referred to like it were harmless, but it might be a subtle hint for another level, where it indeed can harm you. ¯\_(ツ)_/¯
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