Ditto to all the above. A Comp Cams 268H High Energy cam is about the max a stock-compression street engine can handle without adding a lot more go-fast stuff. Use the reccomended anti-pump-up hydraulic lifters and valve springs to go with it. It will handle 6,000+ RPM without floating the valves that way. Use a roller-type timing chain and the corresponding sprockets, along with a thrust button that keeps the cam from "walking" back and forth and changing ignition timing a couple of degrees by varying the distributor gear rotation. Restricting the centrifugal advance in the stock HEI distributor by about 5 to 8 degrees and adding the same amount to initial timing will give you a better holeshot without creating excessive timing advance on the top end. I like 2 1/2" exhaust pipes and Cadillac mufflers with both inlet and outlet pipes the same size. One muffler can handle a 500 cubic inch Caddy engine, and dual pipes with those mufflers are quiet, and act like straight pipes where back pressure is concerned when paired up with a 350 engine.
Jerry

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