Average power applies more to co-generation than to a platform. The prime power rating is most often applied to islanded loads such as a platform. The highest rating for a given set will be the Standby rating. The Prime Power rating is typically 80% of the standby rating.
You can often find the information on the Manufacturers website.
The information may not be given directly. You may have to compare engine and generator end numbers to find an equivalent set. In your case, knowing the description of the sets will make to search easier.
Bill
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"Why not the best?"
Jimmy Carter