If you don't have a shut off valve you might consider running the tank volume low. Fuel will run out the tank side line when you disconnect it from the pump. I don't know how high the tank is on a 48 compared to the pump but on my 38 I can flex the end of the line up and hold it in place with a length of cord to keep the gas from running while I'm working on the pump if I'm at about 1/4 tank. Also, if you find you're having difficulty getting the bolts to start because the lever on the pump is holding it too far out, rotate the engine to get off of the cam lobe. It can also help to use a longer bolt to draw the pump up tight & put the regular bolt on the other side. When the pump is tight to the block you can remove the long bolt and put the normal bolt in place.