No, you don’t need to remove the injection pump (IP) or oil filter housing. Indeed, doing so would be a major task. You can unbolt the plastic VCV on top of the injection pump and swing it out of the way for a better view, but not required. There are 4 bolts which take a 10 mm wrench. A ratcheting box wrench will make the job much faster. There isn’t enough room for a socket wrench, as I recall.
A trick in removing and installing the shutdown valve is to angle its body towards the engine block since there is a smidgen more room on that side to clear the filter housing. It also helps to suck in the stem w/ a hand vacuum pump, but that might not be possible when the diaphragm is torn. Otherwise, push in the stem with your finger.
Yes, it is important how you insert the new shutdown valve into the IP. The vacuum port should be up. The L tip must go past a flat lever, so that it can pull backwards on the lever (can’t see it, but imagine). That lever is closer to the engine block. If angling the shutdown valve in from the block side, that should happen naturally since the tip should then slide past the lever. If correct, you will feel no resistance when pushing the shutdown valve to seat on the IP and should feel it pull on the lever as you move it back. If you must force the shutdown valve forward (compressing its stem), it is then pushing on the lever (incorrect), which would cause high fuel flow and a high-rev’ing engine on startup which could cause damage. Not much to fear since it is fairly straightforward and common sense. You will need 2 new gaskets with the shutdown valve, one on each side of the factory metal spacer.