Boats all came with options. Different engine packages and generator packages. There is no single generator as 'standard'.
Do you have the serial number?
Is this a Diesel generator?
Often two models close in Kw output are using the same block. The output difference is in the board and circuit breaker. For example a 5Kw Koehler and an 8Kw Koehler are the exact same generator with different controllers.
I suspect the Westerbeke 8kw and 12 are probably the same.