The motor mount/backplate/flywheel part is because non PS motors need to sit a pinch lower so the flywheel can contact the starter box wheel through that slot (thats what its for!!)
The ones that say you need to cut the crank; there are two types of cranks. SG and standard. Disassembled they are easily told apart. SG is longer, smoother, and only has about 1/4" of thread on it. Threaded cranks are noticeably shorter, and the entire length is threaded. For non PS applications, you will want th SG shaft. Hopefully this helps