Gary,
Davis sells their traction control boxes, installed in an MSD ignition box. The unit itself, is about 2"L x 1 1/2"W x 3/8"Thick.
These things have upset the racing establishment to the point of the development of electronic traction control detection equipment to give pre-race inspectors a heads up.
Apparently, a lot of NASCAR guys used to have them, until stiff fines were imposed. Some still use them on road courses, when they can get away with it. Their comments, from an independent source, are all positive, albeit anonymous!
Bill