Let's See Your Lathe

[f350ca]

Nice score!
That's an adjustable threading die on the back. There should be other cutters for the different threads per inch. From the look of them they appear to be easily sharpened by grinding the end.
You, need a spanner like this for the chuck.

Only bigger. I cut these on the cnc plasma table, just did one for a friend's Colchester, can't remember the size. I made one for my Colchester, burn't it out with the torch and ground it to fit.