I don't know about the 6s but the original 8s had a heat control valve on the pass side exh manifold like you descibe(I can't see your link). All it was was a flapper of sorts held closed by a spring that relaxed as the manifold got hot. in the cold position it would be up and as the spring relaxed the knob on the end of the shaft would move down till it hit the stop at the full open position.