Is this a generator? 600kW @ 0.8PF works out to 2082A @ 208V. If you use a 2000A breaker, you won't get the full rated kVA, but that might be OK depending on the power factor and linearity of your load. If you need the full rated 750kVA capacity, you'll need a 2500AF breaker and can use the adjustable trip to get what you need. Be aware there are some other considerations for larger ampacity cabling between the genset and OCP, and often requirements for other protective relays like reverse current and over/under frequency.
This is getting rather large for 208V. If this is new construction, would 480V make more sense? The generator is the same (series vs parallel connection of the windings), but it makes the switchgear, cabling, breakers, and ATS a whole lot smaller and cheaper. Really depends on the nature of your load; there's something to be said for not having a bunch of distribution transformers, too.
