On all of my old tractor.. I'm sure many of them started life on ND oil. I have moved all to HD oil. I did it with short change intervals.. and extra filter changes.
Cheapest for me was to hit wallmart and buy lots of cheap 30w oil.. change it.. run it a few hours.. as soon as oil darkens on the stick.. change it and filter.
My JD B took ? 4 or 5 changes over a period of a few weeks to get it to run with clean oil...
Soundguy