I ran across this conversion while studying up for my 72x2 belt sander build. I have my treadmill all broken down and ready to go. Here is a smithy conversion I found pretty neat.
https://www.youtube.com/watch?v=IDItLgwDrwo
I want to get an old band saw & drill press. I will convert them over to a variable DC motor. I think I will go get another treadmill today.