I have a 11A 68 built and I do not have.
A portion from the link:
Usage of the valve was not consistent. 1967 Camaros receiving the valve were all models with C60, all SS396 models and NOR-built Z28s (at least the later ones). However, the 1967 LOS Z28s did not get the valve. At the start of 1968 the C60 rationale was dropped and the application of the valve generally changed to all models with 12-bolt axles. One exception is that starting in mid-1968, NOR Z28s stopped using it for a year, starting again in mid-1969.
And note that usage of the valve on 67-69 Camaros was apparently not related to J52 disc brakes.
Different opinions have been expressed on whether or not it was effective at reducing stoping distance but CRG has not seen any comparison braking data. If it was effective, why wasn't it used on all models, and why was Z28 usage irregular?
Several have suggested that this valve might have been a reaction to a consumer lawsuit in prior years, and therefore, it's application on vehicles may not have been entirely rational. This remains undocumented speculation. In the meantime, we are searching for more data on this valve and on cars that have it (and don't).