K-H brake swap done, but doesnt stop!

Garrett Ellison said

Here is a link that will help you out. It should be pretty obvious if it’s the problem if you crack the line open on it that goes to the rear brakes, you should have fluid immediately.
1970 - 1976 Mopar Combination Valve Autopsy | Muscle Car Research LLC

Click to expand...

So if i unscrew the rear brake line at the prop valve and fluid comes out, its fine? Is it a common problem with these prop valves to block the fluid to the rear? I hope its not that as its total hell to get to!