With that kind of torque, I'd opt for plan D, E or F whatever we are up to by now, and that's to take it somewhere to have them fix it, paying the bill maybe cheap compared to major injury or death if things go wrong, if something slips or breaks while doing this project.................................. but that's up to you to decide.
I've used and own a torque multiplier, but after the reaction bar started to slip on where it was placed once, sweat started to run off my forehead and the oh sh@t factor kicked in big time, that pucker factor also kicked in and the moment of truth came, do I attempt to back it off or keep going or where could I jump fast enough to avoid flying debris, then I noticed the reason for the problem was a socket that popped and cracked, as they say no good options at hand, but at that moment, I'd have given any amount of money to have anyone else holding the breaker bar other than me, preferably at another shops location with their insurance involved and I'd have gotten a call later to inform me of the outcome. Nobody got hurt...........luckily but every time I go to use it, I ask myself, just how much is this project worth to me and do I really want to do it that badly myself. Just a thought to ponder a while before putting that kind of torque on anything, as they say things do break, go wrong and bad things happen faster than you can blink.