Ok, the answer to the 500 error was to edit /etc/apache2/conf.d/modsec/modsec2.user.conf and add the following limits which increase max upload to 2G, then restart Apache.

Code
SecRequestBodyLimit 2097152000
SecRequestBodyNoFilesLimit 2097152000
SecRequestBodyInMemoryLimit 2097152000
SecRequestBodyLimitAction Reject

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