An update:
Thanks to the huge generosity of Jon, a 250 200 series tool holder now sits on top of my WM 180!!!
I decided in the end to mill off the 22mm (approx.) base that the existing tool post sat in on the top slide. That was going to be far easier than seeking to bore the hardened steel of the battleship sized tool holder on the 180 . I then drilled the top slide of the lathe with a new 14.5mm (turned down) drill which would fit my Saupe BF400 miller. Its a small machine, and I was anxious about its ability as well as my own, but it coped easily. I then tapped the hole, and the M16 post screwed in beautifully.
I have no doubt that the tool post is overkill on my little lathe, but its solid in the extreme, and it will centre the tools, and still articulate around the axis of the post without fouling the cross slide which I was concerned about. Thus, job done, and a boost in confidence to me along the way!!!
If I can work out how, I will post a picture, but the lathe is now akin to my Labrador wearing Pit Bulls huge black leather Studded collar!!!! You have the image I am sure, but it works well, meets the intended purpose of convenience, and is versatile.
Many thanks to Jon again and to all who assisted. I am very pleased with the result.
regards
Andrew