a non running antique vehicle doesn't have a time limit on it, you'll just hafta get it inspected b4 you can register it, and you will not get it across the border without "importing it" .... you might also import it as "parts" .... note also that now you have to make an appointment [72 hours ahead I believe] with US customs to take a titled vehicle out of the US, and you have to send the title ahead so they can check it - miss yer appointment and yer outta luck, reschedule and find someplace to store it till the appointment
Bill