I installed mine without cutting the rubber grommet by removing the ignition cap from the ignition cable. Chevs of the 40's has the grommet for sale for $7.99. One cent less than last year.
Wirewall grommet, armored cable Ignition switch to coil The rubber loop grommet, holds the armored ignition cable to the choke cable This is available from Chevs of the 40's for $25.69. Last years price was $24.00. It is installed also by removing the end of ignition cap off of the ignition cable.
If you are not having the car judged I would cut the firewall grommet as Gene has said because I would not want to mess with the ignition cap. Taking the cap off requires removing not only the cap from the metal cable it is attached too but also removing the ignition clip on the end of the enclosed ignition wire.
Under no circumstances should you cut the expensive rubber loop grommet to attach it to the shielded ignition cable. Doing so will cause it to fall off the shielded cable when the choke cable is installed. You could try super gluing the rubber where you cut it, but I am not sure this would hold!!!
I will post pictures later.
Good luck, Mike