I have six months to train for a Deadlift only competition. The only gear allowed will be a belt.
What kind of routine should I be using??
I would suggest you stick with a Westside Barbell routine.
All the various types of squats, GM’s various rack pulls and the like will strengthen you deadlift. Please don’t ignore the awesome pullthru either. Don’t forget to increase the frequency of speed pulls after a dynamic squat set; 10 singles with no more than 60% 1RM.
Find a way to add contrast to the bar for deadlifts was well. Chains work great for this. De-loading the bar via suspending the bar from bands in a powerrack will really train your overload at the top position.
Another thing to consider would be to set the bar in a rack roughly half way between your knees and your lockout. Pull for a 3 rep max. Next week lower the pins 1 space (assuming your rack has 2" spacing) and pull for 3 rep max again. Do this every week until the bar is on the floor. That week, pull for a 1RM. This would occur after your max effort lift except for the last day when it is your max effort.
Do deadlifts and variations: snatch grip, off a low box, from pins, etc.
Heavy rowing and shrugs.
Good mornings.
Grip work.
Squats and quarter squats off pins where you start in the same position as when you start your deadlift.