Fwiw-My wife and I have a pair of 1975 Chicago built Schwinn Suburbans we bought new. They are in great shape and only tires, tubes and brake pads have needed replacement, so no idea on parts availability-probably ebay would work. We get comments from 'bike guys' as they pass us and even buy offers. One guy offered $1000 for the pair.
It can probably be MADE to be ok but I certainly wouldn't add a motor to it as it came from Wal Mart. I'd at least have the spokes gone over by an experienced wheel builder and check the rear axle and set screws. You don't need OEM parts.