If you Google "Old Oak Common Turntable Photo" then there will appear numerous recent (i.e. post-Beeching) photos of the Cowans electric turntable that recently left Old Oak Common for Swanage.  They provide the answer to my question above.  A simple (even rather flimsy looking) steel frame extends across the center of the bridge with electric cables strung from two pylons each side of the well:

https://c1.staticflickr.com/9/8020/7460991028_2b160693b2_z.jpg

I think Legge Lane should have this.

Note the operator's cabin.  I imagine this is a recent addition after steam was discontinued but I have no photographic evidence to hand to say if this is true.  But basically it is fair to say that such "amenities" were very rare on British Railways.

EDIT - Here is a high resolution shot from Flickr:

https://flic.kr/p/akfJ3f

I suspect there are two reasons for the use of Yeovil Junction as the prototype for the PECO kit. First, and most obvious, is that it must be the nearest in situ turntable to Beer(!), and second because the probable designer, Bob Phelps lived locally and was a member of Yeovil MRG for many years. The 'table has been repainted several times in my memory including when it was first restored to use so I would be careful about using modern pictures as a colour reference.

Incidentally, the EH documentation looks remarkably like what is known as a 'windscreen listing' (ok, platform in this case) in the trade...

Adam

Thanks, Adam for the information above. As you will see from my additional comment about Old Oak Common, the various photos there even during just the diesel era show several different paint schemes. During the 1950s there may have been very little paint, though white was used to highlight safety zones, a practice that was, I believe, started during the blackout of WWII.