Only running on 3 cylinders

Removed timing belt to replace water pump, put it all back together and no runs really rough and 3 cylinders down? Well I was having a coolant issue in my 1988 3.0 v6 4x4 nissan pathfinder, and so I replaced the thermastat and the fan clutch and then went to the water pump, I had to take the timing belt off and when I went to put it back on I had to realign the timing marks, I put it back togeather and tried to start it, it didnt want to start so I re-timed it, and wen I started it is really hard to start and when it turns over finally it some times will misfire and idle really high and then low, continuing to vary. And it is only running on 3 cylinders now, the head on the passenger side is totally dead, none of them will fire. I have spark going to all 6 of them. And before I did this it was running really well all six were firing. So I dont know what it would be, so if any one can give me any advice and tips that would be great