This is kind of off topic but would the GEC be run to the CT cabinet or the first disconnect?
Is your Panel being installed in compliance with 230.70(A)(1)? If the answer is yes then for the most part you would only need the disconnect within the panel enclosure. If you install a disconnect after the CT and before the Panel then that is your service disconnect and it would effect what you run and the panel you originally asked about.
In some areas ( not in mine ) the POCO calls for a disconnect ahead of the CT which is allowed but not the norm I would not think.
If your CT is on one side and you are going straight into the panelboard with a 600A MCB and you are meeting 230.70(A)(1) then I would think you are ok.
Others will chime in I am sure.