Well it has bee a bit of a struggle, but I have managed to get the turntable working/motorized.
Step 1 I used the ply offcut from cutting out the turntable well to strengthen the base of the well. The centre was cut away to allow room to get at the wiring tags and the bearing. It is simply screwed in place through the fixing locations disguised by the well "drain covers".
Step 2 I am using a clear case motor available widely on ebay or the web. The case if screwed to a small piece of batten cushioned for sound reduction using a piece of track underlay (thin foamboard will do). The wood will be fixed to side of a batten.
Step 3 Using an overlength batten, I drilled a 4.5mm hole somewhere in the centre, having carefully measured where the motor spindle will be positioned. (check that the hole is drilled squarely). Check that the motor operates freely and if necessary, widen the hole.
Step 4 is the tricky bit.
With the motor spindle temporarily in position, measure where the long batten is to be cut to fit between the frame and cut to length.
Step 5 requires cutting the motor spindle to the correct length. NOTE :- Ensure that the spline on the spindle is engaged with the final gear wheel before measuring and while cutting !!
Measure the approx depth between turntable collar and the top of the frame
Then subtract the depth of the batten to give you the length of the spindle above the batten.
Step 6 I added a couple of offcuts of thin foamboard to reduce noise where the batten meets the plywood circular strengthener.
Step 7 With the spindle temporarily in place, pilot drill 4 holes through the batten for final fixing then open out to take fixing screws.
Step 8 Make a final check for fit and working motor. Roughen up the end of the spindle with some emery cloth apply some cyano glue and quickly push the spindle into place within the collar. Leave to set.
The four securing screws (not shown in the pic) between the batten an the plywood strengthener can be tightened/slackened to provide some slight adjustment if the motor binds slightly.
Because I had added plasticard walls to the turntable well, I found out that the ends of the deck rubbed on the walls in places and had to remove some of the ends of the bridge and shave away some high spots on the wall in places before final assembly and gluing.
However, after lots of trial and error, it all works. I will try and post a video soon if I can figure out how to do it !