I would not run MLS unless the crush area of the gasket lines up w/ the raised portions of your flanges.
I'm in the ultraseal crowd and would follow GM's LS exhaust manifold torque specs. I haven't looked at my headers since I installed them, 0 leaks:
Apply a 5 mm (0.2 in) wide bead of high temperature threadlocker to the threads of the exhaust manifold bolts before installing.
- P/N 12345493 - GM High Temperature High Strength Threadlocker (U.S.)
- P/N 10953488 - GM High Temperature High Strength Threadlocker (Canada)
When tightening the exhaust manifold bolts it should be done with two passes. First tighten the two center bolts on the exhaust manifold. Then tighten the rest of the bolts, alternating from side to side, while working towards the outside bolts.
Install the exhaust manifold bolts.
Refer to the following torque sequence:
Tighten to 10 N.m (89 lb in) on the first pass.
Tighten to 20 N.m (15 lb ft) on the final pass.