At www.everythingselectric.com/nice/ ... we have a nice piece on nice smooth planetary migrations. We learn that Neptune moved from 20AU to its current location at 30AU in a very slow and calm movement. The heavily populated mean-motion resonances in the Kuiper Belt strongly suggests that the orbits of the planets have migrated. This is the so called Nice Model. It proposes the migration of planets from an initial configuration long after the dissipation of the proto planetary gas disk. The Nice Model is used in dynamical simulation of the solar system to explain such events as the Late Heavy Bombardment episode, the formation of the Oort Cloud, and the existence of populations of small solar system bodies such as the Kuiper Belt, the Neptune and Jupiter trojans, and numerous trans-Neptune objects dominated by Neptune. The Nice Model is the currently most popular model of the early solar system - but is not universally accepted.
Having said that the Nice Model may explain the Velikovsky movement of the planets - accept that mainstream relegates changing orbits to the early solar system. This is a ploy they use to distance themselves, and ourselves, from anything nasty happening in the solar system.