From: Gregorio Garcia Karman <[log in to unmask]>

>1. playing a mono half-track open reel tape on a stereo machine and
> reversing the channel playing in the wrong direction digitally.

Flip the reels over to play the other side like they did "back
in the day" and you don't need to mess with digital manipulation.

>2. playing a full-track mono tape on a stereo machine.

Don't sum the channels.  That may add distortion.  Use the
best sounding channel.