If you can get your hands on a 4 bolt main 350 that would be the better of the two. If all you have is the 2 bolt main, you can have a machine shop drill the holes out for you. That might cost a...
According to GM Shop manuals Cylinder Head Bolt torque is 60-70 ft-lbs. I have found that if you follow the procedure to progressively increase torque in 20 ft-lb increments as you follow the torque...