To create a neck support like mine you will need the following. (Sorry but since I am in Australia, my Measurements will be in mm's)

1 - PVC Pipe Flange internal diam 55mm (nominal - mine is 56mm)
1 - Length of PVC Pipe internal diam 51mm External diam 56mm
1 - Length of PVC Tube (or plexiglass) internal diam 44mm external diam 51mm
1 - Rubber Lift Boot
1 - 60mm diameter expanded spring (cut to length)

The Flange


Using the brain cup as a template, mark and trim the excess material from the flange, the sand it smooth on the edges. I rounded my edges to give it a "softer" look. After drilling the holes for the 5mm bolts, I sanded (1200 grade) the flange to "key" it for the primer. I used Testors Grey model primer followed by Plastikote Chrome 613. The flange looks a little dirty here as the plastikote chrome tends to show up finger prints. Take a hint, use gloves when handling anything painted in plastikote chrome.
Support Ring The  support ring is really just a packing spacer to make a snug fit between the main neck piece and the flange. My piece is about 25mm wide (1 inch) this gives a good support and it is a very snug fit
Neck The neck consists of plexiglass tube. Mine is about 300mm in length and passes through the radar and collar assemblies. Notice the hole drilled into the side. This is to allow the cables for the lights to pass out of the tube before it reaches the bottom. The bottom of the tube will have the hankshaft motor attached to it (for the crown). The hole also provides access to the brass joined that joins the crown drive shaft to the motor.
Assembled This is what it looks like assembled. Although I have not pressed the parts together fully. I am not using any glue on this at all. The fit is tight enough. You can if you wish use glue. In the back ground u can see the lifter boot. This gives you some idea as to scaling.
And now the boot   To fit the neck into the radar, you will need to sand the shaft hole so that it is slightly larger than the neck support. The Radar assembly provides a very good guide for the neck. To allow for movement in the neck with out "scracthing" apply a small amount of vaseline to the inside of the radar hole. Do not use grease as the chemicals in grease may have a negative impact on the perspex (plexiglass). Place the boot over the neck support and glue the top of the boot to the neck support (snugly fit it up to the flat part of the flange) (see pic) only use a small amount. I used polyurethane for this job. If you wish you can now place a 60mm diam expanded sring over the neck shaft (this will give you a spring loaded action for the bubble lift mechanism)
Into the Radar We go That is it.. Insert the neck support  into the radar assembly and you are done. If you press down on the neck support, it should just bounce back up. The length of travel will be dependant upon the length of the spring used. (this pic does not show the completed assembly - obviously) but by now I am sure you get the idea.) I did not glue the bottom of my bubble lift boot. I used doubled sided tape (so I can remove it if need be)

Once the assembly is totally complete I will post pics of the bubble lift mechanism.

Mounting the motor. I just cut a retainer ring out of pvc pipe. By cutting notches into the retainer  the hankscraft motor is held in place. This picture shows the motor secured to the neck support. Inside the neck support is a brass coupler joining the drive shaft and motor shafts.