UPDATE ON CORTINA SPRINGS | YES THEY WORK!!!
Ive used the front springs from a 6 cylinder cortina. Brand new Super Low King Springs with a factory drop of 50mm. They have only been tested on ra60 and I'm unsure of a61/63/65.
My only issue when putting the springs in is that the rubber hat for the top of the spring does not fit quite right. The hat is a touch big, however you could cut a small piece out to make it fit, then Id say tape the hat to the spring.
The springs have NOT been cut and have been located properly. Factory spring rates for these springs are 350lbs (roughly 6.2kg/mm). Unsure of the king spring ones, however Im pretty sure they are progressive rate.
Also a quick video to show how stiff the springs are when I jump on the rear bumper.