This lathe is a Boxford TCL acquired for £350 and I have used the existing structure , steppers and motor drive / control..
Effectively just added a pair of cheap drivers and a BoB and a bit of my own time (Which I dont count ) so total outlay on the machine is still around £400.
Cant really justify outlay on exotic motors so just something to play with until I get the confidence to invest in something better.

With regard to spindle indexing, the original Boxford spindle sensors did not stand up to the process, and with some unsuccessful experimentation and with some well considered advice from a friend, a different type was chosen which has turned out to be well up to the job. Correlates well with the measurement using a mechanical tacho so i am happy to use this and accept the reading which it gives me on the screen . Fluctuations seem to be only a digit or two in a thousand so good enough for my purposes.

I was always told that I would not be able to thread successfully with Mach but it looks like I will just need to discount pulley ratios too.
Will just play a while with what i have then look at changing to linux. I chose to keep Mach 3 cos i was familiar with it , but looks like it falls short on a 64bit operating system.

Thanks for inputs anyway.