Was the original run even in widescreen?
No, but how is that a problem? HD is about resolution not aspect ratio.
I know if I watch the original DVD's stretched to fit my widescreen, obviously it's stretched out, but it looks good. No pixelation.
But there's not going to be any extra "width" to the scenes the way some other live stuff might have if it was cropped to be 4:3.
What is films natural aspect ration anyway?