cam for 340 street car

XE268 cam, lifters and springs would be a good upgrade for your application.
At least have the heads bowl hogged to get rid of all the casting material obstruction under the valve seat. Then blend to get rid of remaining humps and bumps. Gasket match intake ports of the heads to be equal too or slightly greater than the exit of the intake runner. Blend the port back into the runner 3/4" so you have a smooth, unobstructed flow from the intake runner of the intake manifold into the runner of the head. Grind some off the pushrod pinch point, as that is one of the major limiting factors in head flow on small blocks - the pinch point. This head work is not difficult and the benifits are tremendous.
If you have a 71 or older 340 with the so called 10.5 CR this should give you around 375hp and around 400 if you went to headers. either way, you will notice a difference in the seat of the pants.