2 would be a lot easier on the tractor, and I suspect if you're plowing with a 60 year old tractor, its more for fun than production, and getting a little more "seat time" wouldn't be a bad thing.
An Oliver 77 diesel is what started me as an Oliver fan. I was trying to disc a rough field with an 8N, and getting the puddin' pounded out of me. Neighbor brought over his 77 diesel, and insisted I use it- And the difference was night and day. Tall, long and smoooooooth- rode like a Caddy by comparison, and I love those 6 cylinders.