Early ones before it was incorporated in to master cylinder. I'm not 100% sure if any front rear splits retained it. It would have been confusing if you had a rear end pressure failure that could be shut off by hammering the pedal hard enough to close the brake limiting valve.
The early ones I was referring to were in the single system, prior to the split tandem set ups, though, the early shut off valves will work fine (but not ideal) in a front / rear tandem set up, just do away with any other valve in the system first.
