Regarding the vent tubes from the valve covers - each side runs up to a "y" and then the single line plugs into the rear of the air cleaner assembly (not the carb itself). You may need to buy the "Y" and some generic vacuum lines - but it all standard auto parts store stuff.
Any old round air filter works. They are really cheap. You just need to match your air cleaner size. McMike has a sophisticated engineered air cleaner and I just run the standard 11 inch Edelbrock. We both seem to do ok.
I double what Doug said about getting newer EFI heads with a better compression ratio.
As far as tuning - I tweaked my carb (Edlebrock 1404) with different needles and jets until I was blue in the face. I was never able to generate a significantly better result than the way it was tuned out of the box new (but I was able to do worse).
The only problem I have is when I go off road and drive at severe angles. The carbs do not run well when tipped - even with the special off road floats and springs installed. Once you get back level - everything is fine again.
1980 Stage One 109