I have a 91 Mercury grand Marquis and I have an 84 what would I have to do in order to use the trany out of the 84 in the 91 both are aod but different linkage conections.

You can change the linkage from trans to the other by pulling the pan . You should check to be sure that tail shaft lenghts are the same they do have 2 differant lenghts and also the drive gear teeth for the speedometer you need to count teeth on the gear on the shaft otherwise speedo might be off. Other than this it should work.

Good luck