When it was popular to add cruise controls, back in '73 or so, after the national speed limit came to be 55mph, I thought that would be neat to do to our '66 Newport. I found an independent shop in Lubbock, TX that was doing the Perfect Circle/Dana cruise kits, which were pretty much factory-correct for Chryslers anyway. No problem, they said, as a '74 kit would work.
I then went to the local Chrysler dealer out there, Fenner Tubbs, and talked to a tech out there that had done many of them. He said the major thing would be to enlarge the rectangle that the turn signal stalk went through. He took a ball point pen and marked mine, which basically put the area to be removed forward toward the instrument panel from the existing hole (which would become twice its width. To clear the electric wires which came out of the stalk. From there, just making the connections with the '74 factory cruise accessory kit.
I then looked at the new '74s at the dealer at home. The more I looked, I saw the same spatial relationships/measurements in that area of the two cars were pretty much the same. Steering wheel to cowl and cowl to carburetor. Which meant the speedometer cables could work, IF they had the same connections on each end between the '74 and '66 (which there probably were not the same, but the length probably was very similar). In other words, the architecture of that part of the car was close enough for things to work better than suspected, as mentioned. Would not have bothered me that the turn signal stalks between the earlier models and the '74s were different (although the '66 had the dash-mounted controls and a completely different factory system). But, never did get it done. The marks are still on the steering column "bowl", though.
Find a good C-body donor car, for the wiring harness, brake switch, and turn signal stalk. You might plan on getting a rebuilt cruise transducer and/or vacuum diaphragm/cable assy, IF the one you find might be aged too much. Be sure to get the throttle cable linkage AND the Lost Motion Link at the carb, from the donor car, too!
I always did like those Chrysler cruises as they had "memory", plus "resume" in them. Ford had those, but it took GM until the early '80s to get there.
Enjoy!
CBODY67