"I only ever found that single drawing "
There are several drawings in various books. They are all redrawn from original sketches in
(1) ShipsCover 624 Armoured Cruisers 1940
(2) Johns workbook 1941 [Drawings in Workbooks are simple sketches (not draughtsman's drawings) about 6in wide]
The differences arise from a 1941 decision that the ships should have a silhouette similar to (and so could be mistaken for) KGV battleships.
These original drawings are all held at the National Maritime Museum's Historic Plans and Photographs department at the Brass Foundry, Woolwich Arsenal.
I have seen all these drawings. Had there been a proper 1/16in = 1ft Sketch Design drawing, I would certainly have bought a copy.
The best redrawing of (2) is Len Crockford's published in 'Building for Victory' by George Moore. See EDIT below.
The best redrawings of (1) are in Raven and Roberts 'British Cruisers' p269 where both the 12,500ton and 15,500ton designs are redrawn.
These drawings are not to scale, and figures for dimensions on the relevant legends should be used, rather than any derived from measuring published drawings.
None of the above drawings show internal arrangements, nor underwater profiles. Friedman's drawing must be based on his interpretation of written discussions about things like boiler positions and armour.
As for the turret design, everything is speculative, as the turrets were never built, nor even a design completed. I'll offer some comments:
The turret was a new design, and so was the gun, intended specifically for these cruisers (and a 1939/1940 range of designs of around 10,000tons, on hulls limited to Southampton length by docking restrictions, chiefly at overseas bases. There are no drawings of these designs, only a table in Cover 624, reproduced in George Moore's article on Cruisers for the Royal Navy in Warship 1997
This MkIX or MkX gun was to fire a 290lb shell with a muzzle velocity of 2670 fps, compared to the Counties' 256lb at 2805fps.
The Counties' twin turret was designed for an elevation of 70 degrees, and a high rate of fire, leading to a complex design. The MkX for 45 degrees and much lighter and simpler. (ie, not based on turning the Counties twin into a triple.)
Gun and turret design was undertaken by Vickers, not the Admiralty, so Admiralty Sketch Design stage drawings do not necessarily accurately represent the actual turret designs, which were not usually finalized at Sketch Design time. Vickers triple 6in, triple 6in high angle and quad 14in of that time were all 'square cut' and it seems very likely that the triple 8in would have followed suit and been an enlargement of the triple 6in. It is not a question of fitting 8in guns into the existing triple 6in. An 8in turret would be over twice the weight of a comparable 6in.
EDIT
A few further thoughts, having looked more carefully at Crockford's drawing in 'Building for victory' redrawn from the drawing in Cover 246.
Its caption says 2as sketched early in 1941. It is therefore NOT a drawing of a ship with a silhouette similar to KGV. The four twin 4inHA shown each side, indicate that this is the 1941 16,500ton version, of March 1941.
It also differs from Raven and Roberts' drawings ,which represent the 1940 design stage, in that the hangar is shown in the 'Southampton' position alongside the rear of the bridge.
Crockford also draws turrets with the length of the exposed barrel rather less than the length of the gunhouse.
That would be true of a triple 8in turret based on the triple 6in, but differs from the turrets drawn in Raven and Roberts. Friedman follows the layout in R&R, which represents the 1940 drawings. Do not assume that this means that the turret design was actually changed - see above.
Not to scale: R&R's 12500 ton is drawn virtually the same length as their 15500ton version. Waterline lengths were actually 610ft and 670 ft, a difference of 10% or 0.5in on the drawing. This shows in the difference in the sizes of the turrets in plan view, which ought to be the same. Blame the publisher's page layout designer.
I suggest, GarlicDesign, that as your gun barrels look to scale to around 10m, that is right for a 50 calibre 8in, but your gunhouses might need to be a bit longer.
See for example
http://www.google.com/imgres?imgurl=htt ... FAodeQsNEA
And (but not all the barrel length is shown)
http://www.google.com/imgres?imgurl=htt ... FAodbTAPcA
As drawn in R&R and Friedman turrets are not simply a direct expansion of the triple 6in, but whether they correspond to any actual Vickers design is doubtful
The book drawings are all small and sketchy, but if I had to trust which ones were most likely to be accurate renderings of the originals, I would go for Alan Raven and John Roberts every time.
EDIT 2
I've looked again at my photos of W John's Workbook.
There are two attempts at designs for a 3x3 8in cruiser. Both are very basic outlines, dated 1939. Both are for ships 580ft waterline, and therefore relate to the 10,000ton ships with Southampton size hulls.