I suspect it would bolt on. The same unibody front and suspension. The difference is the body lines at the doors are different. That could cause the doors to catch on the fenders when opening.
I seen the 65 Rancheros that have the comet fronts on them. They match up with the trim lines and actually look good.
If you are really thinking of doing this. Measure the trim and body lines and where they match up by the windsheild.
I never saw it done on a Ranchero that early. Good luck.
The front end will bolt on, there is no problem with the doors. The doors are an interchange, except for the stainless trim holes on the Comet. There is a little issue with mounting the headlights, there is no clearance bulge for the 4 headlights on the Comet frontend. I remeber I guy doing this same swap on a 62 Ranchero in the 80's. He also did a Lincoln F/E swap on a 78 Ranchero that looked really nice.