I have just got the Mike Foot big vert 20 week plan and ready to start it this week or next week. From reading the sessions the plan has and reading what you are saying about your training history and races, I would say if it isn’t an ‘A’ race for you then you will be able to fit it into the plan as one of your long training runs, then make sure and take an easier few days after it, or as long as you need to recover, especially if it is a de-load week after so you can absorb the training gains.
With this being in 9 months time this gives you lots of time to build a strong base of training and begin to layer in elements of speed closer to the event. Since it is quite long away it may be good to consider some other races before then too if you have time for this as it will be hard to work towards a peak performance until then and maybe some other races you could target to spread the volume of training out and keep it varies for you. Sounds like a really cool race though with those stats and must be some big climbs in there! Lots of time to get some really good quality training in there