The NEC considers the 600A disco the service disconnect since there are more than 6 tenant disconnects and a house disconnect. But the OP said the utility does not want a separate production meter so meters are going to have to be back fed. Most multi-meter panels can't be tapped between the meter and the downstream CB. The PV system is too large to back feed any single meter. The OP has not be specific about what meters will be back fed so it's hard to provide further guidance. Most likely the OP is looking at an expensive panel upgrade, talking the utility into a production meter, or dropping down the size of the system.