Actually, I think stages 7 and 8 might be a lot easier to map than you fear. You just have to go with maps that follow the "gameplay" rather than the exact structure of the various layers of platforms/clouds.
For stage 7, I'd use the layers of the slow platforms as the base of the map. It's clearly not when you see how fast those metal rings go by as well as when you reach the end of the tube, but it's a stable structure around which most of your movements are centered. For the faster moving platforms, I'd simply place each one at the approximate height you're expected to use them to go from a slow moving platform to another since that's all they really are, moving steps expected to be used at a specific moment. Since the metal rings seem to be part of the actual background (unlike the platforms which are all sprites), they're probably spaced 480 pixels apart (which is how tall the background contained in the name table can be). As for how much space to leave between the last platform and the end of the tube, I'd just fudge it as long as it's a multiple of 16 pixels.
For stage 8, I'd do something similar. First off, I'd see if the cloud platforms between the airships appear in a set, repeating pattern if you wait before using them. If yes, I'd simply fill the space between each ships with pattern found. If there are no patterns and their positions are random, then simply use whatever pattern you observe and use that. In my Battletoads maps, most of the high speed levels had randomly positioned obstacles so I simply made patterns that could be repeated without looking like they did too much. It's not perfect but it works well enough.
