I’ve got to the last 7 weeks of the Big Vert. I am training for a 2700m 28km race but due my location I often cannot get this kind of consistent gradient. I am now regularly running routes of around 30km and 1500m of ascent, including technical climbing up to grade 3 scrambling. In my opinion you probably don’t need to adapt this program, if your body can handle it, it’s pretty comprehensive and pretty intense.
If anything I would maybe look at completing it this year to give a big uphill base, and using it again next year as a top up. Last year I based most of my training around it, even though my race was cancelled and I took time out to recover from COVID after week 3. It gave me a much better insight into my own expectations within the plan.