exhaust leak

[worldofme]

couple questions about exhaust leaks and exhaust sytems.

first off, I'v got an exhaust leak somewhere near the exhaust manifold and after replacing the exhaust manifold gaskets I'm still getting a leak and can't quite pinpoint it's location. I noticed a leak under the valve cover and I'm wondering if it's possible that leak could be making the noise that sounds like an exhaust leak?

I have dual exhaust on my truck and each side runs straight from the exhaust manifold, down to a muffler then down the rest of the truck. I've been told that on dual exhaust I need an exhaust pipe connecting the two and I want to know if this is true?
Also, I don't have any catalytic converters on either side and have been told in some cases they aren't needed but I live in California where smog checks are required. Do I need them and if so do I need one for each side or just one on one side?

this is all for a 1977 Chevy K5 Blazer 4x4 350cbi. Any input would be greatly appreciated. Thanks