Look online for a Delco EST ignition for the 3.0L Mercruiser, it's a complete kit with; distributor, coil, cap, rotor, spark plug wires and should come with instructions on how to wire it up. Best bang for the buck as it comes with everything and you'll need, except maybe a couple feet of wire and some crimps, $250 or so. I put one in my 72 140 HP and haven't done anything to the ignition except replace plugs - twice in the last 7 years...
You do have to re-wire the shift interrupt switch as the points system uses ground and the EST uses 12V (wire the shift interrupt switch to 12V). The resistor wire needs to be bypassed so the ignition gets full battery voltage. Also, you must follow the proper timing procedure for this type of ignition, put in base timing mode and set to 1* or 2* BTDC, so it's at 10* or so out of base timing.
There are Pertronix ignition modules to convert your old points dizzy to electronic ignition, but all the stuff I put in bold up top does not come in the kit... Probably $80-100 for this kit. (Worst bang for the buck.)
