You might have to guesstimate the ratio by estimating the pivot point to the pedal in a straight line, without regard to the shape of the arm through the floor. Then meausre from pivot point to the adjusting rod.
Another common cause of a hard pedal is too much preload on the master cylinder. Be sure you have a small amount of freeplay in the pedal before it starts to compress the piston in the master, or the brakes will be partially preloaded and make the pedal firmer. You can check this by grabbing the pedal with your hand and pushing/pulling and watching the adjusting rod to see if it has any clearance. Or disconnect the rod and see if it has play in it.