I'm narrowing down my choices. With the 6MR500-NDY-4 fit in brackets without having to grind off the edges?

 

Yes sir they will work without grinding them.
The only thing you may need to do is open the mounting holes up on the speaker to get them to line up with the threaded holes in the brackets

 

So make the holes larger? Not bad. I was expecting to have to drill holes in the speaker to match the bracket. Are the stock holes matching with the 7.1 holes on the brackets?

 

the ones that i have installed bolt right up, there are 2 different sets of holes in the BT brackets, sometimes covered up by the gasket material.
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I could only get 3 bolts in mine until I enlarged the holes.