Proportioning Valve - keeps the rear from locking up.
ebrake and/or line locks - it sucks having your truck chase you down the hill.
new rear brake lines or live with some ghetto loops.
you may need to weld in some clips to tie down brake lines.
pretty detailed write up on the spidertax install at http://www.off-road.com/suzuki/tech/traxdisc.htm
You might take a look at the Trail Tough kit, uses subaru rear calipers, lets you keep a normal ebrake. I think of that disk hanging low off of my driveline whenever I run up on the belly armor.