That would depend on the year of Granada. Later models had rack and pinion steering, so its intirely possible that they both used the same spindle.
An easy way to find out is to go to a parts house and check on the part number for the 80's Granadas with front steer, and compare it with the part number for your Mustang II. If its the same part number, you are good to go. If they dont match up, take your spindles back to whomever you got them from.