My opinion is that loosening with an impact gun is fine. Tightening, well... you really want to use a torque wrench and you'll need to lock the flywheel somehow to do that.

As an aside, I think the concern about reverse rotation (in moderation) is overblown. Engines frequently turn backwards a bit on their own fairly often... on a failed start attempt, when shutting down, etc. I think the only time it is truly dangerous is if the chain/tensioner/rail system is already worn close to the point of failure. This is just my opinion, YMMV!

__________________
1987 W201 190D