Keep the butts separated by at least a couple of inches and go with the low and slow method. The key is a good meat thermometer. It doesn't have to be an expensive one either; just a simple plunge type one will do but be sure to NOT insert all the way to a bone; you don't want bone temperature, you want center meat temp.
Low n slow brother!
By the way, during the last hour of cooking:
1. Slather on a blackberry jam (no seeds), honey, & brown sugar mixture
2. Wrap the pork in foil
3. Put back in the smoker for about an hour bringing the temp up to about 300 degrees
4. You have just sent your pork butte over the top.
I've had it turn out several times with a purple ring. The only problem I've encountered is having leftovers for the next day.
Low n slow brother!