Prop Audio System Mount with Adjustable Magnetic Brackets

I'm a member of the Rebel Legion here in Washington state. Our local groups (501st Legion, Rebel Legion, Saber Guild, Mandalorian Mercs, Droid Builders, & Dark Empire) usually setup a Star Wars Experience at Emerald City Comic Con. This includes various props and displays presented for our guests to enjoy. We collect donations for our local children's hospital.

Here is a video of what we presented for ECCC 2023
https://youtu.be/eY8Bjf9Omd0?t=1343

I have previously added electronic lights and sounds to a few of the props featured in our Star Wars Experience. I wasn't slated to build anything new for the props this year until our meeting about three weeks before the con. I was asked by the project lead for the Speeder Bike build if I could add sound to the bike. I had parts available from another build, so I agreed.

The project lead requested a sound unit that could magnetically attach to the bikes frame. I requested the dimensions of the frame I would be working with, but h