When a replacement bridge is too heavy for a M of W crane especially where the location is not practical for contractor access the Engineering Dept will get an assist from the Mechanical Dept and one or more of their wrecking cranes.
I have seen pictures of wreck cranes removing old and installing new turntable bridges.
I even recall when one wreck crane crew overturned their crane, another of the railroad's "Wreckers" was sent in to retrieve its fallen comrade. The second crew made proper use of their outriggers and performed a successful recovery!
I would keep one "Special Work Train" (politically correct term for "Wreck Train") on the layout. Even if only standing ready, it will make a good conversation piece. And just for "fun" it could be dispatched to an adjacent (unmodeled) divisiion to assist another wreck crew. At times these trains also operated off their home road to help out a neighboring road.