At last someone with the same problem i had!
I did a thread on this as i did my previous 172s subframe and my current one needs a clutch. Theres one or two you can get a spanner in, as theres cut outs for this - but im thinking the one thats spinning a b*****d!
I did it by cutting 3/4 of a square, peeling it back, puttin a spanner on the nut and then eventually welding the cuts back up