Wasn't sure if I should post this here or in C&V, but here goes...

I recently picked up an older Campagnolo Athena (might be Chorus) sealed bottom bracket as shown in the photos. This particular model has two identical cups with no flange or lip on them. The threads run right to the edge, with nothing stopping them or making them "bottom out" against the frame flange.

When I did a dry run on each side, to make sure the threads were nice and clean, I noticed that I could keep screwing them in until they starting going well beyond the edge of the frame.

So when it came time to do the actual installation, as feared it was problematic to tighten them down, without a hard stop to use as a reference point. When I would tighten the right hand cup, the left hand cup would start to spin, and vice-versa left to right. The BB is Italian, so this meant that one would loosen as the other was tightening.

I have the appropriate Campagnolo splined tool, but only one of the. I was able to generate some torque by holding up the opposite side with needle-nose pliers, but I didn't trust putting 70nm of torque on it with just the pliers on the other side.

Is there some trick I am missing? Do I need to but a second splined nut to hold the opposite side in place while I torque one side to spec? Can someone with some experience on this offer some advice?

(For the record: I'm putting anti-seize on the threads, although I don't see how thread-locker would really solve this problem with that much torque)