Although I can't answer the LIM part, I can lead you in an easier direction if you are willing to spend about $80. KNEX now has a newer coaster called the Screamin' Serpent (which you're probably already aware of). Instead of a single car that flies any which way it can, you have a 3 car train that is locked to the rails with guide and upstop wheels. I have already made numerous designs including elements like cobra rolls and heartlines!!!!
This would at least let you experiment with something that will follow the track well. The track gauge is different than that of the original, but you can use the same pieces to combine kits. The only requirement is that you use the green "x" crossties that are necessary for the new Serpent train to operate. The wheel assemblies wrap around the outside of the rails, akin to a real Schwarzkopf or Premier shuttle! Your biggest challenge may be pushing the train since there is a significant amount of play between the wheels......it has a slight shuffle to it.
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Thanks for riding Tidal Wave and enjoy your day here at Marriott's Great America!!
www.angelfire.com/oh4/tk173