Can anyone help decode Mopar distributor numbers?

If you like the old one, then put on a new nylon or steel bushing.

If the tag is still on the side, its probably not been through a rebuilder and you can look up the advance specifications in the shop manual for that year. From that you can plot the expected timing curve.

In general, a 318 2bbl will have a timing curve that advances quickly in both stages.
While in general a higher rpm engine like the 340 will have an advance that slows more in the second stage.
Smog era distribitors for CAP/CAS have quick and longer advances above idle rpm than earlier non-smogged equivalents. This is to compensate for the retarded initial timing for CAP/CAS.

The way to return to a non-smog curve with magnietic pickup distributor is to weld up the inside of the slots and then you can set the initial timing to pre-smog (10-12 BTDC for a 273 4bbl). I've posted phtotos and diagrams - you'll just have to search for them.