If I towed on a daily on Asphalt, I would lower a 2 wd dualie.
But as a tow rig. I would never compromise the frame with a c notch.
Get a half ton If you wanna get super low. If you reay really want to get low as you can without ruining the structural integerity, visit suicidedoors.com, and get their heavy duty 4 link kit, and triangulate it they are pretty long and super tough. Relocate leaf springs. Or use semi air bags.