[Hindmost]

Aluminum cups and lock ring? Yeah it's a problem.

Just know during initial adjustment there's going to be several trial and errors so don't take things to full tightness, just very light tightness at first. Try not to use much force on the cup, just hold the position of the cup with a wrench and only move it after releasing the force from the lock ring. And only put full force on to the lock ring when finalizing adjustment. The slotted washer should prevent rotation of the cup for the most part. (Make sure the slotted washer can move freely up and down the steer tube. Carefully file the inner surfaces of the washer or clean up the steer tube if it doesn't.) Full force just has to be pretty firm, not wicked firm. The size of the wrenches give the impression that you use mega-torque. If there's space try putting masking tape on the faces of the wrench flats.