I've been searching for a speedo cable for my 1980 Indian. It is a square drive cable with the same threaded connectors on both ends. It screws onto the little sender unit on the front wheel and the back of the speedo. I found the same system on an old sears exercise bike. I am going to check the length tonite, but it looks promising.
If anyone is looking for a speedo cable. Check out some yard sales, the dump, etc. for one of these exercise bikes.