60mm especially in the 2nd and 3rd rows. My guy is crazy good and could probably do anything requested.
I did mine starting with a 300D pod and built on it from there, added the second row then the 3rd. He could have done the whole thing in 1 piece. It is a track car so don't care that much about looks but he could make a very pretty one piece unit.
Any competent high end stereo shop should be able to fabricate anything u want.