I'm going by memory here but Monolith mixes 5x5/3/1, PR sets, Widowmakers, BBS (up to 15x5 IIRC) and some of the assistance stuff is optional.
This means that on some days it pushes more the main work (anchor), sometimes pushes more the supplemental work (leader) while assistance is left to the trainee's discretion.
It's my 0.02 but I see it more like a challenge, you prepare doing 2-3 cycles of something appropriate then run Monolith.
Out of the Forever templates, Pervertor comes to mind, it has things that can prepare you mixing strength and size.
Otherwise, since Monolith is 3 days a week and focuses on squats, deads and press, look up the Full Body templates, there's a few that do exactly that - focus on squat, deads and press with 100 chins/rows as assistance.
After Monolith, I'd follow up with one cycle of something lighter (5's Pro + FSL), but that's just me.