Just something that fits and works well. My rear one is smaller around 5x7. Where did you find yours? I'm a bit limited here in Aus as to variety. I'd prob have to source from eBay.
I found this at local stereo installation shop. I told him what I needed to do and he walked right over to his shelf and grabbed this. I posted 1/2 of the wrong pictures above.
Www.retromanufacturing.com