Roar approved just means that they can be used. You need to find a class that actually lets you run them. Check with your local track to see what classes they run. If they have a modified on road then the ones you use may be all right.

The cars you listed should all be able to fit the systems you want to use. I have a TA05R and use a GTB in it with no problems. The GTB is larger but fits.

Most 2S lipos with hard cases designed for car use and roar approved (must be hard cased) will fit in the area that a 6 cell stick pack will fit. You may need to have higher battery posts or use a velcro strap instead but it should work as long as the chassis doesn't use a saddle pack.

As for weight, you may need to add some lead weights to balance the car but they are available at the hobby shop.