I love "Mr. Scott's Guide" and its first-rate drawings, but even Johnson couldn't resolve some design riddles (such as how to fit in the two photorp bays
indicated in TWOK). I agree with Okuda's comment in the intro to the 1701D blueprints- "the Enterprise
is not that photographic miniature, is not those sets, but rather it's a creature that lives...in the minds of the viewers." So perhaps there can never be just one answer as to its scale.
That being said...David Kimble's production blueprints show the bridge dome as 1/8 the width of the saucer, and Johnson's bridge drawing
indicates the wall-to-wall diameter is nearly 3/4 of the dome (and half that for the 'pit' railing). So given the traditional ship length & width of 1000x465ft, that works out to about a 40ft-wide room. And that fits with the scale on Johnson's drawing, which indicates a 20ft wide railing and about a 38ft wide room.
Of course, as the old pirate said, the 1000ft length is more what you'd call a 'guideline'...