Can I run 6-500kcmil and 2-350kcmil use-2 wire in a 4" grc conduit for line side power to a 600 amp disconnect

What does your foreman say?
What do the prints say?

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The quick answer is no. And you also may not be able to use 500 parallel for a 600A 3-phase service either.

Do you own a code book? All of this can be found in about 30 seconds in a code book.