Depending on what the course looks like (mostly rolling long sustained efforts or punchy short hills), I’d recommend:
SSB 1 & 2, - General Build, - XCM Specialty
If your race has more singletrack than gravel roads, General Build is a nice mix of sustained and higher intensity efforts. I use the above plans for my MTB 100 mile events. However, in my area the races are 90%+ singletrack with plenty of punchy sub 5 min efforts.
Would suggest to build up endurance a lot. 170km will be a very long day on a MTB. If you can average 20km/h on a mtb, and I think thats really fast, you´ll be riding 8.5h. If you can average 15km/ happy 12h day waits for you. So go out and ride endurance and endurance and some endurance. Then as mentioned before, some VO2Max. If you have a long steady climb maybe more threshold power. Depends all on the profile you´ll be ridiing on that day. and maybe some technical skill rides a week, if you have some time left