Valve stems are a measured 11/32, I thought they were 3/8, but I measured them when I had the cam housing off. All the OHC L6's were 230's in 1966 & 1967, and 250's in 1968 & 1969.
Duration numbers I figured were all measured at .006" per some old literature.
Looking at my 1bbl cam that I took measurements off (the sprocket picture with the degree wheel behind it), it looks like about 180º of duration at 0.050" on the intake, which is subject to error of +/- 10º IMO between my lash adjuster compressing, how I measured and how I've eyeballed it to the degree wheel. I have a measured ~240º at first measured movement and the spec's say 228. As mentioned before, the OHC design also fast ramps the valve. When I have the engine apart I'll probably look at taking measurements at 0.010" lift increments to see the true slope of the valve acceleration. It appeared very fast, and actually looked like closing was faster than opening, but then again I was turning the cam directly rather than the crank so the valve events were moving twice as fast as I'm used to with my V8's. Real measurements would settle the question.
Advantages I have going for me are, I'm not turning a water pump, I'm not pushing a mechanical fuel pump (you should feel the difference in turning the accessory drive!!) and my timing is far more tightly controlled as well as fuel distribution should be as well. I don't have tuned headers, but I do have a fairly opened exhaust, at quite a bit more so than OE. My turbo cam has a bit over 260º duration with a bit more on the exhaust side.
I'm hoping to get mine to a chassis dyno at some point, should be interesting. The turbo engine I'm hoping to engine dyno it before installing it. As a friend of mine says, RPM is king, get the head to flow and wind it up, and that is my plan, watch for the point of diminishing returns and shift there.
Two fuel pumps because instead of a sump in the fuel tank I'm running a surge tank, but the surge tank requires a lift pump to get fuel to it. Then the high pressure EFI pump pulls from the bottom of the surge tank. This is so it doesn't hiccup when intermittently sucking air when low on fuel. I use the OE mechanical pump on my Skylark instead of an electric. And speaking of which, the lift pump gave me fits on Thursday, so I ended up taking the Skylark to CA. So I may be changing out the fuel system in the car while the engine is out. Move it all over to the driver's side and get the pumps and stuff in a better spot.
Rebuilding an OHC Pontiac 250 with EFI and a Turbo