you didn't need headbolts; which brand are they? if their chinese shit I would not use them since they may not be made to spec. headbolts in BMW's do not need to be replaced when doing headgasket, there was no manufacturing error. Usual suspect in headgakset for bmw's is because of inadquate cooling whether the thermostat, waterpump or Fan was not sufficent.

get 101 performance projects for your bmw. it's 20$ at barnes and nobles. it shows everything you need to do step by step with pictures.

101 Performance Projects for Your BMW 3 - Google Books

or if you feel lucky heres the digitla version el oh el.