Yes the 70SS 396/350hp had the TCS. Yes, it is generally thought that it hurt performance. We all know the story about the guy who stripped his car of anything that he didn't think was necessary. If it didn't help you go fast than it was trash.
The parts of the system that I know about
Solenoid - right off QJet carb, part vaccuum & part electrically operated. Effects vaccuum advance of distrib in all gears but 4th gear (for a 4sp. That is what I have, so that is what I've researched.)
Switch - On transmission. I believe is switched "ON" for 1st, 2nd, & 3rd and "OFF" for 4th.
TCS relay - on firewall connects tranny switch with solenoid
Ground Up Restorations is the ONLY source I've seen for the Solenoid. Their catalog has some pretty good illustrations of how it sets up on the valve cover and even shows you the special vac advance line clip you'll need (has 2 line running on it rather than 1.) They are a small operation, so don't expect things to go as smoothly as with Year One, but they are very good guys who will talk endlessly about your car if they could. I talk to George.
PO Box 3402
New Hyde Park, NY 11040
Hope this helps.
I just checked their website. The TCS Solenoid illustration I reffered to is on the first page of their "Detailing" Section.
[This message has been edited by michael j (edited 02-01-99).]