Fine tuning an L-82

[fnsjr]

I have a 1980 L-82 auto which is factory stock. I was planning to install a cat test pipe and wanted to know what jetting and timing changes would compliment a lower restriction exhaust system. I also wanted to add an open element air cleaner. I know they are less restrictive than the factory set-up and sound great but will there be any performance benefit, or loss, given the fact that the engine will no longer be drawing cool outside air? I also have one question concerning an existing problem. When accelerating from a stop, the engine stumbles for a second and than accelerates strongly. This only happens when the engine is warmed up. The engine also idles a little rough. Any ideas?
Thank you for all your help, Fred