I keep breaking rocker arm bolts, help please!

Why am I having trouble torqueing down the rocker arm bolts? Its a 340, original x heads ( have been cleaned and magnafluxed) and I'm using the original bolts. I oil the bolts and start torqueing at a lower torque value and work my way up to 30ft/lbs. I've broken two off in the drivers side head. The other side I cleaned the holes out and used a tap to clean the threads (I was told thats not what you're supposed to do, but I'm at my witts end). I get to 20ft/lbs fine, but when I move onto 30ft/lbs all the bolt does is turn. Any ideas? Am I doing something wrong? Please help, im tired of drilling bolts out.! Thanks