So, coming back to this, after working on a few other modifications.
With the QCTP fitted in it's existing condition, the centre stud is not quite long enough, so I need to make a new one:

As I temporary measure I found and cut some 10mm threaded bar.

The QCTP has a plate that it sits on. This plate is machined to fit the raised centre section compound slide:

However, it is a sloppy fit and has some play in it, so I propose to replace it.
Trying to get the tools centred I have noticed that for some even on the lowest setting some tools are still too high?

As tools vary, I may need to make a couple of new base plates?
I have also noticed that base plate is slightly wider than the tool post, which stops the tool going lower:

However due to the sloppiness and shape of the base plate, some tools can be made to go lower, to make them on centre, this, I guess, is bad practice.

So question, when making a baseplate for this tool post, should it be wider than than the tool post or can it be flush?