Firewall penetration for Rotax 914 loom bundle info request

I am working on my firewall and placed the Turbo Control Unit inside the cabin on the firewall and now I need to make a penetration to get the bundle through to it with the plug which is BIG, 3" X 1 1/4"

(72 X 29 Mme). I am requesting how and where other people placed this penetration, any tips on restoring the strength, patch with smaller penetration encompassing, etc. 

Thanks for any tips.