A:  I don't think we can be of much help. We design and program the computers that control roller coasters, not the mechanical parts. We do computer models of roller coasters to aid in the calculation of ride capacity and brake timing. Mechanical engineering companies do computer models of the forces and speeds, potential and kinetic energy, and frictional losses. In the roller coaster industry we don't actually do physical models that I know of. Maybe someone does. The computer models are probably as accurate or more so, since it would be difficult to get the frictional losses right on a model. In the real world things like the temperature and condition of wheel bearing grease have a big effect on train speeds and total track time. I've seen trains not make it all the way around on the first run of the season, which is usually a very cold day, meaning that the wheel bearing grease is stiff.  The train will get stuck in the valley just before the tallest hill after the lift hill. I've had fun helping them winch the train out of the valley.  

The only thing that comes to my mind as a good way to make a model would be to use a marble or steel ball on a track made of two pieces of wire separated by about 3/4 of the diameter of the ball. How you would make and bend that wire track is a tough question. 

I could point you to a video tape of the history of one old classic coaster. The tape talks about the design and some of the physics involved but it doesn't get into the science too much. 

Maybe one of the roller coaster companies (mechanical engineers) could help you more. Arrow Dynamics, B&M in Europe, Intamin. Check the AIM, TEA and IAAPA web sites for information on these companies.