As long as your goal for the 50 km is in line with where your training is at, it would be doable. What to do with the 6 weeks (now a bit less) until then is the question, and my thoughts only reflect how I would approach it if I were in your situation. Subtracting for a period of recovery/taper before hand then this leaves less than 5 weeks, and ramping up both distance and vertical simultaneously can be a tall order. How to balance those (endurance, vertical) also depends somewhat on your strengths/weaknesses in those areas – that is, what will give you the most payoff over the short timeframe.

I am more comfortable (psychologically as much as physically) having confidence in my endurance first, and for me a few dedicated vertical sessions go a long way. The idea of running the 32 km course with 1500 m vertical as a training round sounds good (and like a good day out on its own), because it hits both of the points: one, it would let you know if 50 km would be a stretch and you could make the switch in race distance if it feels like 50 km would not be a good idea; and two, based on your comments that maybe your vertical training thus far is limited, it would prime your quads for the downhills on race day. If you don’t have the vertical base, then this would possibly destroy your quads for a few days or more, so best done 2 weeks out from the race in order to be recovered. That would leave less than 4 weeks until then, over which time endurance might pay off more, but with some hill sessions to prep for the training round on the 32 km course.

Anyway, an interesting challenge as to how to approach it!