Re: '66 Evinrude 80hp
No, the Ford/Mercury coils did not have a resistor built in. He could use any ford coil from the 60s - mid 70s, I would think. However, with today's menu driven parts look up systems, you need a year, make and model to look anything up.
of course, if you get an older guy to help you, you can just say Ford coil from a battery - points/coil ignition system, and you will get the right one. The OP probably wants to get a matching condenser (likely .25Mico Farad), just in case the OEM one is some wierd value.