1. Yes it replaces both.
2. If you use the same coil you still need the ballast resistor to reduce the voltage so it doesn't overheat.
Better off to do the HEI module and a C, D or E core coil, as they are made to use a full 12v.
You'll also get the full benefit of the HEI spark, which allows up to an .050 gap on the plugs.
In a bit here I'll try to post some more info on that for you.
