I've never liked working on the floor - bending down gets old even faster than I do. I recommend lifting the mower up onto the bench and working on it there. It's way easier to see what you are doing. Yes, you often have to move it when you need to make a part or disassemble something in the course of a project, but with a little planning, that will only happen at the end of a stage of the process. For example, you start with the mower on the bench (I usually take the handle off, so I can rotate the whole mower without anything hitting the wall) and strip it to the extent necessary. Then you have an engine and a frame. Put the engine aside, and get the frame up to scratch, on the bench. (If you have to make parts, you put the frame on the floor while you do so.) Then put the frame aside, and work on the engine. When it's finished and you're ready to run it, put the frame on the bench, fit the engine, and take the assembled mower outside where you can run it safely. Personally I don't run engines unless they are bolted to their frames, it can get too exciting.
