340 General Rebuild Info- Cam Recommendations

The two stage advance important. More so with electronic ignition and always when using vacuum advance - which other than drag racing is very helpful for all off idle part throttle efficiency and power.

Two stage advance has the timing advance very quickly from idle to 1400-1800 rpm. Then advances slowly with increasing rpm.
The Chrysler design does this well.
An example here 360 Tune Up
Its important to make measure the actual timing like Rockable did before deciding this is the modification needed.

This thread has a good example of making other adjustments. Also shows both types of spring perches Chrysler used.
https://www.forabodiesonly.com/mopar/threads/distributor-curve-help-needed.496183/
Examples of how Chrysler changed the timing, in particular the initial timing and rpm, to improve emissions at idle in this post.

The secret advantage of the heavy spring for high rpm when using electronic ignition.