Are you archiving, dubbing, printing??
Are you using a software based editor? (final cut, adobe)
It’s always a matter of settings when ‘letterboxing’ is used.
Are you printing to tape from the computer or from a camera?
Sounds like your box is trying to cram 720×480 into 640×480.
Let me do some digging and I’ll try to see what you’re up against.
Keep us posted in the mean time!
Johnny C