Rear hold off valve

[rs1]

Did these come on ebodies ? The one I am talking about is bolted to the frame rail roughy under the driver's seat

 

[rs1]

This pne

 

[floyd]

I believe that’s an early 70-only thing for E-bodies. Here’s a link to the repro mounting bracket:

Early Build 1970 E-Body Brake Valve Strap

 

[EV2RTSE]

I agree with Floyd, only used until Jan 1 1970 apparently.