Would help if you show us which vise you want to mount.
This is not my MFT bench, but I wanted to have my machine vise removable. So I mounted 3 steel plates to the bench structure, under the benchtop, and tapped 3 holes in them. The steel plates are retained by big flat-head wood screws and are mortised into bench structure. On the left side of the bench is a big wood vise, and I made sure the rear (fixed) jaws on both vises were co-planar. Comes in handy sometimes for long work-pieces.
So I have 3 screws to remove the vise. Actually, I have never needed to remove it.