I would like to mount a 2000W/100A inverter/charger in the gasoline engine compartment where the current 60 Amp charger is. That way the battery cables are already there. Can I use the existing cables for the inverter/charger?
Inverters are NOT ignition protected and CANNOT be mounted in a gasoline engine compartment. Boat manufacturers go to great lengths to make sure that engine compartments are vapour sealed from the rest of your boat, since gasoline as a vapour is extremely combustible. Never install any device in your engine room that is not ignition protected. Otherwise, you will endanger your life and the life of anyone around you.
Also, you’ll need to look at the size of the existing wiring. I doubt that your 60 A charger has 10/3 AC wiring. You’ll definitely need 10/3 wiring for the AC side of the 2000W/100A charger.