Pretty easy if I remember correctly.
Remove the original door handle by unscrewing the two large self tappers holding the arm rest to the door shell.
Screw on the new arm rests using the same holes.
The top part of the arm rest will make a dint in the door trim where it wants to sit. Mark accurately.
Remove arm rest.
Where the alignment mark is drill small pilot hole thru door trim and into door shell (but ot into the door skin!)
Find an old escort front door/s and remove the bayonet clip that is pop riveted to the door frame that holds the top part of the arm rest. Drill your door to suit and fit the bayonet clip as it was on the old escort door.
Drill out door trim to suit. Fit door trim, fit arm rest.
Like falling off a log!