Thanks for writing in to us with your questions. You can certainly use the 24 week plan you already have for this race. As you know the aerobic training in it is done on foot and can be done running. If you have not been training for a while I’d suggest doing a 12 weeks of less structured running base work just to get back to where you can run almost daily for an hour or so. Then when you begin that plan you’ll get the most for it.
If you want more structured guidance I’d recommend using the Luke Nelson intro to ultra plan and extending it by repeating the first 12-16 weeks. The first time through those weeks you should use a much lower running volume than is suggested. How much lower?? Try 50% of the suggested. This will give your body a chance to become accustomed to running regularly again before trying to follow the plan as written.
I hope this helps,