The 2 pin resistor is the one that you, in all probability, will be using. It is .5 ohms and is actually the same one used with the points distributors. It is the one needed for use with the 4 pin electronic ignition modules, which is most likely what the Mopar Perf or other aftermarket modules sold today will be. The 4 pin dual ballasts were used with the earlier 5 pin factory electronic modules. So, unless you pull a module from a boneyard car, in which case you would also need the 5 pin wiring harness, you will be using the single 4 pin ballast.
You can also use the coil for the points ignition with the electronic system. The coils actually were the same part number for several years.
I changed my 383 over to electronic a few years ago and have never looked back.