Thanks BB, you have far more experience with broken SB45 chassis rails than I do, and your comments will be useful ultimately in figuring out how to proceed with that part of the project.
Jen, you have done considerably more work on this project than I realised. I'm sorry for mentally classifying you as a dillettante. The reason to inspect the interior of the air cleaner was in case it had flooded with oil (through the breather tube) when the machine was being transported laying on its side. Please put it back together, and remember for future reference, you cannot run that engine without the air cleaner's central screw in place: it plugs a hole in the carburetor.
The next question is why there is alleged to be no spark. The IPL tells us that your engine has the old type of "kill switch" (ignition-off switch) consisting of a piece of aluminium, pivoted at the bottom on the cylinder head, which can be tilted so the top of it is pressed against the metal top of the spark plug. To run, the piece of aluminium is clicked into the position where it does not touch the spark plug, and to stop, it is tilted so it touches the spark plug. Not very high tech, and it sometimes gives you an electric shock when you snap it over against the plug with the engine running, but you get used to that (I don't say you get to like it much, though). Please disconnect the spark plug lead from the top of the plug, then remove the spark plug. Reconnect the lead to the plug and hold the plug's metal base (not the cap where the lead is connected) against the cylinder head. While holding it in that position, pull the starter handle briskly. Simultaneously, watch the gap between the electrodes at the base of the spark plug, where the thread is. See if there is a steady string of sparks between those electrodes. If there is, "We have ignition!" If not, we have our first malfunction challenge.
