From the 1/2 scale blueprints (
The Blue Box Project), the Tardis (full size) is 97 inches tall and on a 54 inch square base (2464 H x 1372 W x 1372 D mm) - OO scale size brings that down to 32.4 H x 18 W x 18 D mm
Other sites give other dimensions for the Tardis, including
http://tardisbuilders.com/index.php?board=24.0 where original BBC props drwaings are to be found!
Another bonus with the Police box is that a local friend used to be in the Metropolitan Police force and has an original key that I can replicate
Update on the K2 - As it happens, the internals of the K6 were taken from the K2 and about the only differences were a subtle change in the shape and material of the telephone. The original phone was aluminium and had slightly concave sides compared to the later phone made from bakelite with straight sides. The dial on the phones were different colour, but essentially the same design.