Since FSL refers to the % of the first work set and SSL to the % of the second work set, and since Leviathan has 70-80-90-100% for work sets every week, I did it using always 70% for FSL and 80% for SSL through all weeks.
Going by memory here but I think I did 10x5FSL for press, 5x5FSL for deads, 5x5SSL for bench and 5x10FSL for squats.
Worked good and didn’t give me any issues, if your TM is correct and you don’t screw your recovery in other ways (lack of sleep, not eating enough, too much assistance etc) you can handle those %s.
Obviously, feel free to lower the % to whatever amount is better (i.e. down to 50-60% for BBB).
As a generic rule of thumb, you might want to push one lift with volume work (BBB, BBS, Widowmakers) and the opposite lift with strength work or dialing it back (SSL, FSL). This is especially true for lower body lifts, doing BBB@70% for 6-9 weeks straight on both deads and squats is the kind of thing that can bury you.