My lathe is an Engineers ToolRoom BL12-24. This is very similar to the Warco BH600, and the Chester Craftsman.
I adapted a Vertical Slide for a Seig SC6 to fit on my cross slide. It is pretty easy.
Removing the Top Slide and Front Toolpost reveals a 25mm hole. The dowel on the bottom of the SC6 Vertical slide is 10mm, so make up a hollow dowel 25mm OD and 10mm ID (Put in a M6 tapping, so that you can extract it afterwards. )
I used brass, for the adaptor, to minimise any possible damage where it would bear on the Saddle, when the Cross Slide is moved.
You will need to scribe two fresh fiducial lines, one to align with the graduations on the Cross Slide, the other for the height adjuster Handwheel dial.
The bad news is that only one M8 Capscrew will be accessible to pick up on the "nuts" that clamp the Top Slide to the Cross Slide. (It will need to be longer one than those used to secure the Top Slide )
The article, giving further detail is on Page 34 of MEW258 (September 2017)
Since then, I have drilled the Base and upper half, and inserted a rollpin, before removing the three M6 capscrews, to separate the two parts to fit a second M8 Capscrew,. After clamping the Base in place, the two parts can now be reunited in alignment. (There is already a dowel between the two parts, so only one roll pin is required to retain accurate alignment )
Howard