Besides replacing the head gastkets, what else are you trying to achieve by tearing it down? Are you having a valve job done? Not a bad idea since you have it pulled this far apart. Machine shop can extract that broken manifold bolt for you while they have the heads.

Do your best to keep everything very clean. If you can get a tap and die set, use it to clean out the headbolt holes and head bolts.

Put some gasket sealer or loctite on your head bolts when you install them. Torque them down in 20 ft lb steps using a circular pattern starting in the middle. Find the type of head gasket that doesn't need to be re torqued, or be sure that you do retorque after about 5 hours of run time.

If you have specific questions, ask away. Hope this helps.

By the way this is the first time I saw your request for help

Pat