It has taken me a while but I have finally got the QCTP installed on my lathe. Probably a total of about 4 hours work but has taken me a fortnight to find those 4 hours.
I needed to put a shim under the toolpost to get the tools up to centre height. I wanted to keep the spigot lug on the topslide so that the original SCTP can be re-installed, so I found a suitably sized bit of round unknownium to make the shim. Discovered as soon as the tool touched it that it is in fact cast iron.
   

Having made the spacer disc to the estimated necessary thickness, it was necessary to mill the spigot to a matching height
   

I didn't have a 22mm tap to thread the spigot hole, so i decided to use the existing 5/8 UNC thread which required making a suitable stud with different sized ends. Had an odd hold-down bolt witht he same thread as the existing toolpost centre bolt so I cut the T-end off it, turned it to size and threaded it to the 5/8 UNC required to go in the topslide hole. I seem to have lost the photos I took of that job, but here is what i ended up with
   
Unfortunately the lever pointed the wrong way and I didn't have any appropriate size washers to put under it to make it point in a more suitable direction.

I found that I had miscalculated (misguesstimated) the required shim thickness and the toolpost was a bit too high, the holders were nearly bottoming out when at centre height. I decided to lower the setup by .300". In the process I decided to clean up that horribly worn surface on the topslide. Putting the topslide in the lathe would have been an easy way to do this, but only having one lathe meant I had to make my first-ever use of the rotary table in the mill. Took me ages to set it up with the spigot centered on the rotary table, partly because the thing is so low geared it takes ages to make a revolution to compare indicator readings.
   

The surface cleaned up nicely with a shoulder mill run up to the edge of the spigot.
   

I milled the top of the spigot down the .300" whilst it was in the mill, then put the topslide back on the lathe and refitted the old SCTP so that I could turn the spacer disc down to the required thickness.
Bunged it all together and adjusted the toolholders to centre height, now they are all close to the middle of their up/down travel. I abandoned the idea of using the old lever nut, think I'll make a nice domed hex nut to suit one of the old megaspanners I have lying around.
this is where I finished up tonight before my steak-cooking skills were required.

   


Thanks again Arvid

One minor issue remains; the piston pad on the boring side of the QCTP is a little proud of the toolpost and only a couple of the tool holdrs have a deep enough throat to actually go over it.
   
I think I need to take a couple of thou off the thickness of the piston pad. A surface grinder would be the best tool for this but I don't possess such an animal; will have to ponder this, can't see myself getting back in the workshop for several days anyway.