This is cool.....The "J" model was only built from September '48 thru January '49. I'll bet your's was built right at the change over period & got the new handlebars & dash plate. It could have been registered as either year, depending on when it got sold. The J was a short lived transition model.
Your bike is the first official "J" in our registry. Send me a PM with your details (real name, handle, state you live in) & I'll get you added to the registry.
Mike Sal