5/3/1 and BBB Assistance for Rugby?

I am currently entering off season for rugby and need to up my strength quite a bit for my position. I am a tight head prop and have weakness in all 4 lifts.
Bench- 275 max. .DL- 365 max. . Squat- 275 max. . OHP- 155 max
Will following the boring but big assistance give me everything I will need for strength or do I need to add another assistance for all main lifts?
For conditioning I will be doing hill sprints.

How long is the off season for Rugby?

In general, BBB shouldn’t be the “main” part of your training. At the most 6 weeks; ideally 3 weeks.

Majority of your training should be 5’s PRO with FSL, 3-5x5. Bar Speed is king.