Here is what I did on my 71 Demon 392 swap. 2" hole and a Jegs 2" grommet in the recessed area under the wiper motor. I have an aftermarket heater/AC box so my location may not work for everyone. The harness will come out behind the intake and on the inside I'm going to run it under the passenger seat where ill have the Terminator ECU, injector drivers and dash module mounted to an Aluminum plate. In the second picture if you look carefully you can see the grommet riveted in place
View attachment 1716350338
View attachment 1716350339