If you find and use the factory standpipe setup I would advise against running the pipe to the manifold over the top of the valve cover unless you have hydraulic valve lifters, which few trucks did. Route it around the front along with the factory fuel and dizzy vacuum lines. Even that is a little crowded so I routed mine below the thermostat housing.
Regarding vacuum: The PCV will oscillate and cause idle speed to vary if it's set too high and the leakage from multiple throttle blades and loose throttle shafts will contribute to the problem. I worked for some time to get the twin-carb (zenith 228) linkage synchronized and the idle speed set low enough at 600RPM. All seem well now.
However, I have a large vacuum port for the Hydrovac that uses a large, trailer, air-brake tank as a vacuum reservoir, left over from pulling a hay trailer with vacuum brakes. There apparently is a leak somewhere that I haven't chased down yet; and until the air is purged from the vacuum tank the idle is erratic after startup when it's sat for a few days. Doesn't happen overnight. But I think any vacuum leaks will cause erratic PCV operation at idle.
