Ol 58 are you talking instrument cluster or complete dash ?
Ive been toying with the idea of grafting on FC front sheet metal on to an EK ute ,Ive done a lot of measuring comparing etc etc and what Ive seen is that the FC front screen on its lower edge has a much more enhanced curve than EK and an EK dash {in your case} is much larger than the FC because the door and winscreen pillar are placed about 5 inches further back to allow for the wrap around screen .
But in saying that my guess is that the depth of the EK dashboard could be basicaly cut off and welded to the FC somewhere around the windscreen surround - metal sometimes just like you and me needs a little massaging to bring out its true beuty.
The closest Ive come is putting an EK dash into a ford Jailbar truck ,Shortened the dash width and it fitted pretty easy and whats more is that I could walk away from that one with a sly smirk on my face knowing I had deliberately defaced another ford with Holden equipment.