Pete,
Be very careful selecting a case with very tight dimensions, especially from Hammond's line of small steel enclosures. I used one of the 1415 series of steel project boxes to house a transformer once and had to do a lot of "customization" to get it to fit because of the rather large lip that these cases have. The 1415C at 6 x 5 x 4H might work for you.
That said, one of those with a little Mu Metal took care of all of the noise issues I was having with the first beta22 that I built so it does work.
Nate