Maybe keep an eye on ebay for a spare tailstock if the lathe is common, that's what I did with my M300 as I wanted one to convert to a lever tailstock as I do jobs that require deep peck drilling or drilling of multiple items and the screw tailstock was getting tedious with all the winding and unwinding. One eventually came up at an acceptable price so I bought it, turns out I knew the guy as he was a local engine machinist I had used in the past. He had been unfortunate when moving the lathe with a mate and a moving skate had shifted and wasn't noticed so when pushed it fell on its front and wrote the lathe off, he sold all the salvageable parts on ebay to my benefit with the tailstock.
------------------------ People collect and restore the South Bend Heavy 10 lathe so good parts have become harder to find now than in the early 90's when I bought it, and every useful spare part I saw.
Except for the 70 position threading gearbox there's little difference between my 1965 lathe and the one described in the 1914 edition of "How to Run a Lathe". In it the tumbler that drives the leadscrew is called a recent improvement.