If your goal is to simply not embarrass yourself, I would think that the lung and leg training you get on the road and gravel, combined with the skills training you get on your less climb local trails (are there at least SOME steep or technical climbs?) will come together to get you through fine.
I just went through something kind of similar (though less extreme). The trails where I live now do not have much in the way of big climbs/descents, but there are some good road/gravel climbs. I had a trip to Pisgah planned for last week. where we would do lot of 1K' to 2K' climbs. There is nothing remotely close to that around me. Biggest steep sidetrack climbs are really just a couple/few hundred feet elevation. I was worried I was not going to be able to keep up well. However, putting in time on the road/gravel bike to get the climbing in, combined with riding the technical singletrack left me in respectable shape for the trip.