Hello all. I'm bout to do a head gasket and exhaust manifold replacement on 02 TB EXT 4.2l. What size Allen wrench fits the head bolts? I plan to drain coolng system and flush, change oil and filter, replace head gasket and bolts and exhaust manifold and studs and all gaskets associated with. I just replaced all 6 plugs and coil packs, water pump, thermostat, fan blade & fan clutch a month ago or so. Anything else I should replace while I'm at it? Timing chain n cover maybe? Any help would be appreciated thanks.