This is the best pic of the Mk68 Gun Director I've been able to find so far:
Here seen 4/1/88 aboard Coontz (Farragut class DLG - just as ostensibly depicted by the classic Renwal 500-scale kit), this type of Gun Director was, according to WikiPedia installed:
"...aboard Belknap-class cruisers, Mitscher-class destroyers, Forrest Sherman-class destroyers, Farragut-class destroyers, Charles F. Adams-class destroyers, Knox-class frigates as well as others."
Here are a pair of closer/clearer views (of especially the face):
The dish seen in all the above, is that of the AN/SPG-53 radar - clearly, very common on the Mk68 - however there were likely (at least one or two) others throughout the years, as well.
I do not yet have (even ballpark) dimensions for the Mk68 cab, however it is clearly smaller than the corresponding, "WWII"-type Mk37 cabs - which in fact persisted through a series of Cold War variants - and certainly smaller than the "Boxy"-type Mk37s, also from the Cold War. Note as well that the Mk68's rangefinder tubes as well as single viewport are - in both size and positioning - very close if not exact matches to features of the Cold War Mk37s. Likewise, the SPG-53 dish closely resembles those (indeed, many may have been exactly the same dish) used on Cold War Mk37s.
From a model-builder's viewpoint, then, it appears a Mk68 Gun Director could be sculpted quite well and easily from a Mk37 - the required very flat faces being easily chopped using a chisel, and the Cold War radar dish of the latter, if available, used directly - to come out neatly with a Mk68 at- or very close to the same scale.
HTH - or if not, then at least you thought it was pretty cool!