After my nightmarish allison ignition system failure, I put a 140-series blue bosch coil into my Sedan.

I did the same with my wagon, and I made a large coverplate to cover the coil hole, and two big 1-1/2" AC line holes in the firewall. I sealed it all up with 3M weatherstripping goop and finished it off will self-tapping sheet metal screws.

I did not want to do that my sedan (since the firewall was intact), so I took a blue coil found a good balance point and wrapped *A LOT* of tape around it. This made a nice stop for the coil. Then I wrapped a strip of that sticky butyl rubber stuff around the coil under the tape-stop and dropped it in. The rubber holds the coil nicely and plugs the hole while maintaining the stock fit and orientation of the coil. I had a spare ignition socket, and I simply swapped it and ran the new heavy ignition wire though an existing hole in the firewall up to the coil.

Here's a close-up