Where can I hook up an electric choke?

Yeah the blue wire is the usual spot. It's a "run" feed from the ignition switch.
However, choke heaters pull some juice, and they pull it through the bulkhead connector, through the ammeter,through the switch, back down and out the bulkhead connector and up and over the back of the engine to the ballast resistor.That poor wire gets no respect.Yeah the factory did it that way, but the copper now is nearly 50 years old.That blue wire continues to the VR.
I wouldn't run the choke heater off the coil though, cuz the coil pulls electrons through the ballast resistor. Now the coil and heater would have to share that resistor. It will get good and hot, and start choking them electrons down to a trickle. If I had to hook it to that blue wire somewhere, I would hook it to the ignition side of the ballast resistor.But when you do that, make sure the connection will stay good forever, cuz you are the only guy that knows where it goes, and if that connection fails, the engine will shut down. And almost guaranteed it will happen late at night, and far from home, and it will be flipping cold outside.

What I did was run all the underhood stuff off a relay, triggered by that blue wire. Now all that stuff gets fused, full battery voltage.If you do it this way, don't cheap out on the relay.And protect it from heat and water.