Right about in the middle of the exploded view is where you can see the "activator screw". Think of it like the star adjuster screw in a typical rear brake drum assembly. When you apply the e-brake, this activator screw gets cranked by the lever you see on the outside of the caliper. Whether your e-brake cables are hooked up or not, you should be able to lock the wheel from spinning by manually actuating the external lever. If it locks the brake down within its range of travel, then you are in a basic state of proper adjustment. If you get nothing, no resistance, no brake apply, then your caliper is way out of adjustment, with a considerable air gap between the pads and the rotor.
Ways to bring it into adjustment:
1) Get inside of the vehicle and build up as much pressure as you can to the rear brakes. Now hold that pressure and set the emergency brake and release (sometimes up to 20-30 times). Repeat this procedure a few times, and it *should* get itself adjusted up. The key here is to extend the piston out as far as possible with hydraulic brake apply pressure (hitting the brakes and holding). With the caliper piston extended out, and then actuating the e-brake simultaneously, this typically does it.
2) Look at the outside of the caliper to determine which way the lever is actuated when the e-brake is applied. Temporarily unbolt the actuation lever (remove the nut and washer). The end of the actuator screw shaft is now exposed, and you can wind it in the direction the e-brake lever would actuate it until it gets tight. This will manually screw the caliper piston outward to take up any excess air gap / slack. There are multiple index points on the shaft and e-brake lever, so you can then take and reconnect the e-brake lever to the caliper. When properly adjusted up, you should only be able to move the external e-brake actuation lever about half way through it travel range to lock the brake.
3) Unbolt the caliper and then remove the brake pads. Using a disc brake caliper piston tool, you can then wind the caliper piston further in / out (spinning the caliper piston clockwise / counterclockwise, which will bring the caliper piston further out.
NOTE: Methods 2 and 3 should be followed up with method one. If you do not have e-brake cables hooked up, have a helper sitting inside of the vehicle holding good firm pressure on the brakes while manually actuating the external e-brake lever on the outside of the caliper (in lieu of doing such from inside of the vehicle with the e-brake cables hooked up).
If attempts at adjustment do not respond no matter what you try, the caliper has internal issues and will have to be replaced. I have seen rebuilt versions of this type of caliper improperly assembled, where parts from a left hand caliper were installed into a right hand caliper, causing the adjustment attempts to go exactly backwards (!), as the activator screw was cranking the wrong direction - the more you attempted adjustment, the worse the adjustment went - DOH!
The operational theory behind parking / emergency brakes is that they are supposed to be diligently applied every time you park your vehicle. Vehicles with a manual trans seem to always have a decently operating e-brake, largely because the system is indeed actuated most every time a vehicle is parked. Automatic rear brake adjustments in the integral e-brake calipers is not going to happen when the e-brake is not used, so the adjustment just keeps getting further and further out as the brake pads wear, eventually getting to the point where they just about quit working entirely.
The re-installation of the original hold off valve isn't going to do anything for the scenario at all... It may have helped the rear drum brakes catch up just a hair in stock form, but the threshold of pressure was only a few pounds - not enough to do anything for rear integral e-brake calipers being out of adjustment...