I found a good tip on here when researching a similar build. Get a Switchcraft 7 pin panel mount connector and swap the insert with the 3 pin in your donor mic. Now you have a 3 pin panel mount connector for your power supply, and a 7 pin insert in your mic.
This worked perfectly for me and is also cost effective. I wish I could remember what thread this was in or who said it. It was one of the many brilliant minds around here though.