The heads require a specific torque sequence. If you choose to do this yourself, which a mechanically inclined person can, have a shop manual or instructions with you. In a nutshell, the heads must be torqued to 28-31 lb-ft; then tightened 90 degrees, then another 90 degrees; alternating head bolts as you go. What is suggested is that after the initial torque is applied, a straight mark is put on each head bolt, then apply the latter torque sequences. The marks will help you keep track of which head bolts you have already torqued.