Specific to factory spec 340 cams;
Automatic-equipped 340's employed a hydraulic cam with 268/276-degrees advertised duration and .429/.444-inch lift.
70 Challengers with a 340, 4 barrel and 6 paks used the same cam.
it had some healthy duration at .050.
- advertised, 268/276*, at 50' , 228/235* with 114 deg separation for a wide 5800 rpm power band and 44 degree's of noticeable overlap
In 1968 there was a four-speed cam used with 276/284-degrees duration and .444/.453-inch lift.
Both cams used shaft-mounted 1.50:1 rocker arms and connect to the crank via a double-roller timing chain.
There are some tell tale signs as to the what your cam might be; how is the idle, smooth/to lumpy. What rpm does the car idle at when idling? When revving the engine out, based on the tachometer readings, what seems to be the power band?
Just a rough way to determine what cam you may have.
As heminut intimated; the only way to really know accurately is measure lift or pull the cam and have it measured/evaluated.