I will now fill the big gap in the shaft with weld, then spin it down in the lathe and I will be good to go in the drive side of things.
It looks like a mild-steel shaft that's had a really hard life - why not just turn up a new one? Seems more likely to end up straight and true that way. However, we all have our own ways of doing things, and anything that works and is fun, is a good solution.
