That is a very old brass that pre dates the MCB design.

As to the function or need for a wedge, the wedge has a crowned top surface that allows the brass to roll under the roof of the journal box. This prevents concentrating the load at the ends of the brass as the axle oscillates in a vertical plane mostly due to low joints. Journal boxes that are not rigidly attached to the side frame, but have verticals freedom to move in pedestals, should have the freedom at the gibs to to stay parallel to the axle, which avoids the end loading. So the presents or absences of a wedge depends on the truck design.

In the railroad shop I worked in, there were buckets of wooden (oak) journal bearings soaking in journal oil always ready to go if needed. I recall one incident where a car with wooden brass inadvertently got on to a train and went about 65 miles before it was turned around and sent back. It ran at track speed with no problems.