You didn't say where you are, so it's harder to guess what engine you have. If you're state side, and both your RRC and Disco are V8s, they should also both be 3.9 and identical pumps, but apparently not, as you say. In the event the engine is a V*, either remove the bottom cover of the pump and pack it with petroleum jelly, or pull the distributor and spin the pump drive with a drill. You'll need to make up a slotted end shaft about a foot long. I used a battery Vacuum pump (the kind used for oil changes on boats) and connected to my pressure sender tapping.