Back to back LRs or 20-something milers on alternate weekends are decent training, but there is another way. That is to do a small number (like 2 or at the very most 3) monster LRs of say 28 to 36m instead. If you have never gone over mara distance, the simple act of exceeding 26.2 is very liberating and will give confidence that you can finish the ultra. Just a thought.
Navigation on the TT is pretty straightforward. BTW without questioning the course measurement, be aware that on a Garmin it comes out at about 47.5m.
Enjoy the training everyone....