Yep sounds like the ignition coil is still getting power when key is off.
I would start with the minimum wiring to start and run the engine. Like remove hot from battery and run a jumper to coil and jumper to starter.
Get it running then pull the coil wire and see if she stops. then just start hooking stuff up until you find where its getting power from generator/alternator and not battery.
also you can start it up warm it up unhook the battery and then turn off the key as well. That eliminates the battery side and you will know its on generator side.
Had this problem once when putting some aftermarket stuff on the 56 had a hot wire on wrong side of switch and once it was running never shut off.
