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.
ADDED:
One of the cleanest of the HEI coils I have used is this 94-97 Dodge Ram truck coil.
It runs on a full 12v and does not require a ballast.
It also put out a spark almost 2x what the old canister type does, and is close to half the size of a canister coil.
You can either get the pigtail for it, or do what I did and trim the connector section off and solder direct to the terminals.
These coils work perfectly with the 4 pin or 8 pin HEI modules.
The 4 pin modules like you normally see used are a bit messy in my opinion, and don't have weatherproof connectors like the 8 pin module.
The last picture is my own car using the GM HEI coil and 8 pin module with weatherproof connectors.
I also have the wiring diagrams for all of these combos when you are ready.
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