A used cam is about as practical as a recycled piece of toilet paper. Unless you also use the same set of valve lifters from exactly the same camshaft lobe they were running on, the cam will wear out in a matter of a very few miles. The Elgin E-293S cam or the very slightly more radical Melling CCS-1 would be a good choice. Both are usually available on Ebay or from local parts stores like Auto Zone, Advance Auto Parts, or O'Reilly's. The Elgin cam is an exact copy of the solid lifter cam used in the 6 cylinder Corvette and the 261 truck engine. The Melling cam has a little more exhaust valve duration for better cylinder scavenging. Neither one causes low intake manifold vacuum or a choppy idle like some of the "performance" cams sold by the resto-ripoff places. RUN- - - -do not walk away from the cams sold by Clifford, and ALWAYS install a new set of lifters when changing cams.
Jerry
