Ian, you made it. The Granada spindle's lower ball joint hole needs to be re-machined to fit your lower spindle. You may have to have the disk hub machined down to fit in your wheel center if you have stock steelies. I did on my '55 Ranchwagon. Otherwise it's a bolt on. I got the complete braking system off of a '80 Granada, Disks, calipers, spindles, M/C, power booster and mount, etc.
One thought I had... does the Merc have the same wheel bolt pattern as a Ford of that vintage? I know some were different??