Ian. First welcome to the forum you will find it a fountain of knowledge

I have had and converted a Warco WM18 I have also helped in a conversion of a Seig mill. I used Linuxcnc on both.

There is quite a lot of working in doing a conversion.

Personally I would not go with a round column mill like the Major If you can find a mill with ball screws that would be a big advantage when it comes to conversion. Good luck with that tho.

Have a read through some of the build logs and do some research before buying anything. (as you are doing)