I actually just did this on my ls3 pump 3 days ago. I was able to get them to move but couldn't pull them out. I ended up tapping them back and forth until they loosened up, then they came right out. I figured I'd look at the pump and figure out why or why not plug the heater ports. After studying the pump and the water flow, I understand why people run hot. Looking at the pump, there are two sets of holes. The lower holes lead to the block, the upper holes come from the heads. The upper (head) ports are also connected to the REAR heater port. The FRONT heater port is connected to the lower (block) ports of the water pump. So, as coolant flows, it comes from the radiator, through the thermostat, through the block, up through the heads, out the water pump, to the HEATER CORE (back across the thermostat) and to the radiator. Now, if your thermostat has the plate that blocks off the front and rear passages of the water pump, with the heater hose blocked, there's no way for the hot coolant to get to the thermostat to open it, resulting in the car running hot. Make sense?! Some run the ports blocked, but there are a couple different style thermostats available. One has 3 or 4 holes in the block off plate. These holes would allow hot coolant to get to the thermostat with the heater ports plugged (essentially looping them together). I actually drilled a 1/4 inch holes my water pump next to the hole that the block off plate sits in in order to allow the coolant to pass by the thermostat making the thermostat open once the coolant is hot enough. As long as you have some way to have coolant pass over the thermostat, I think you'll be okay. Hope this makes sense.