So I was on fleslider's Vintage Centurion site today looking at the catalogs. If you haven't visited his site, you should. Very good site. Anyway, I had the 84 & 85 specs page opened comparing how the models changed. If you look at geometry of the Competition models in 84, the Turbo, Compe TA and Elite RS, they had the same geometry except for the overall wheelbase and chainstay length. The Elite RS had the longest overall wheelbase. 10mm longer than the Turbo because of 10mm longer chainstays.The catalog lists the Compe TA with a 5mm shorter wheelbase than the Turbo despite the rest of the measurements being the same. Could be a misprint.
Then you look at the 85 catalog and compare those models with the 84s. There was some geometry changes between the years. The Prestige is way different than the bike it replaced. The Equipe is way different than any of the previous models. The Elite had some changes as well. If you compare the IM to the 84 models, it's geometry is closer to the Turbo and Elite RS than the Compe TA. Kind of in the middle between the Turbo and Elite RS. Geometry/ride ride wise, the IM's lineage points more towards the Turbo/Elite RS.