The motion effect has a Scale Parameter. The problem is that 720X576 uses non-square pixels and 640X480 uses square pixels. So the 480 is the number you want to concentrate on. Take the video to 83% of scale and you will be very, very close.
Once you get what you want, you can copy the first one, and then paste attributes to all of the others on the sequence at one time.
Steven
http://www.stevengotz.com