Just keep the board < 5.5" wide, it will fit.
I recommend leaving lots of wire length on the inputs so that if you ever want to pull the network out and do some mods youi'll have lots of wire and won't need to mess with the tube connectors.
On any monitor builds, I've always installed the no-rez after assembly through the woofer cutout, it's actulally not so bad once you get your hand in there
jay