Ask the original owner he is a really decent chap.
Don't turn the whole bar make it like a dumb bell. Turn down in the centre then leave a collar each end.
Just machine the collars. Say an inch wide each end.
Big at free end - headstock needs to come towards you.
Big at chuck end - headstock needs to go away from you.
Hasn't this lathe got a Vee for headstock alignment? Surely it doesn't have jacking bolts as well?
If I recall there is also a lever that switches between metric and imperial so it probably does make sense.I cant make sense of that. 1mm is not 30 thou and 7.5 thou is not 4mm.