How much vert is ‘big vert’?

Big fan of the book TftUA and pod. I have a lot of endurance running behind me, mostly from elite-level orienteering (when aged ~15-35) but more recently from veteran 40+ hobby-level road races from 5K to marathon. I’ve always enjoyed trail running so am considering doing some trail races, starting with sub ultra trail races of around 23-26km but also eyeing up a 57km race with 2000m vert. The route looks fun and it’s only 4hr drive away. I think I understand the principles for building my own training plan but would your ‘big vert’ stock plan be suitable for this kind of race? I seem to be more competitive in uphill races than flat road races maybe because closer to demands of orienteering racing and my running economy on flat asphalt is not as good as my capacity & leg strength? Which elements would you recommend I prioritise in the switch from roads to trails?