Not many have tried the Mercedes 11mm bolt trick on the M54..It probably works, although you're still using alum threads with a ton of torque applied as a DIY'er, not under the controlled conditions of the factory. My vote is use steel time-serts using kits 1090 or 1090BS, which I do occasionally rent out to forum members

Helicoils are not a good solution in this application. They're not as strong as time-serts and they are more likely to be a one-time use. Time-serts, once installed can be torqued again and again.

OP I suggest you do all 14 holes as time-serts...I do all 14 every time I pull a head.

A head gasket on an E53 3.0 is not too bad. You have good access and the car stays on its wheels the whole time. I used an engine hoist to remove/reinstall the Cylinder head while attached to the intake manifold. For years I used a paper degree gauge to measure the 90 degree pulls, but the last few head gaskets I used the harbor freight electronic torque wrench.