It would be a good sign if the Brad Mayeur longitudinal repiar kit, which ties into the rear suspension, was installed. Brad sells it directly as does (I think?) Pelican and others. Everybody I know who has used this kit loves it. Some install it on structurally sound cars just for the extra stiffness.
See this section of Lawrence's excellent 914 web site for more info:
http://www.highway914.net/tech/long/long1.html