There are only three components, excluding the connecting wires, that produce spark. The points and the condenser which are located in the distributor body, and the coil. Points could be "frozen" open or shut, condenser could be shorted out, or the coil could be shot. Any of which could happen after being stored for 20 years. The good news is that any or all of these items are not expensive, and the points and condenser should probably be changed out anyway after being stored for that long. There is a member of this forum, Jack Bahm that has a You-tube channel on Model A's. It seems to me that I saw a video by him on how to bench test each of the components. You can probably find a lot of discussion by searching past posts on the forum.