PCV valve details

My euro GTS is missing its PCV valve disc. The usual suspects don't sell them, so I'm thinking about fabricating one. I've looked at some old threads and it seems it's phenolic, 1mm in thickness. Does anyone know the diameter? I can guess from the diameter of the outlet tube that the disc sits on, but it would be good to know exactly. Some posts also mention a small hole in the disc - any idea how large? I'm surprised there's any sort of hole at all, since I'd think that would cause an air leak into the two small calibrated tubes in the valve body, and thence to the inlet manifold where it could lean out the fuel mixture.

If anyone has exact dimensions and a photograph they could post, I'd appreciate it.

 

I'm trying and failing to understand the physics of this valve disc. If the disc has no hole, its behavior makes sense to me: at speed, a combination of air box vacuum from above and crankcase pressure from below lifts the disc off the valve body so the blow-by can be drawn into the carbs and combusted. If you're at idle, then air box vacuum is low, crankcase pressure is low, and the vacuum from the calibrated tubes sucking air into the manifold from below pulls the disc down onto the valve body, closing it so no gases escape. But if there's a hole in the valve, then air will always get drawn into those calibrated tubes and into the intake manifold, bypassing the carbs and leaning out your fuel mixture. At speed it's probably not enough to make a difference, but I'd think it would affect your idle speed. A hole in the middle seems to negate the entire point of the disc. Doesn't make sense to me - can someone explain?

 

I've fabricated a valve disc out of phenolic sheet - 17mm diameter, 1mm thick, with a 5mm hole as a best guess. I've also hooked up cavis hose to the calibrated manifold vacuum ports, so everything's set up the way it should be. The idle's gone up a little - maybe a couple of hundred RPM - although after maybe 15 seconds or so it settles back down. It also seems to have a bit less unburnt HC smell at idle, although that might be wishful thinking. No drivability change at all. I'm really curious to know what that disc behavior is supposed to be, i.e. when is it flat on the valve body because of lack of positive pressure from the crankcase combined with vacuum from the manifold ports. And at what RPM the manifold vacuum is exceeded by the crankcase pressure, lifting the disc. If anyone knows, speak up!