Dropping the rear of my 64, what to use.

OK, I want to drop the rear of my 64 dart but dont want to accidently drop it too low or lower then my front can go. How can I make sure this doesnt happen? Im gonna be using 17x7 wheels. Im running the Alterktion up front so I can lower the front of the car with the coil overs, but im gonna use leaf springs for the rear. If I get 2" de-arched springs, or 2" lowering blocks and Im using 17 inch rims will my rear still be higher then my front?

I was thinking if i got the measurements from a stock 64 tire and rim combo and the measurements of a 17" tire and rim combo I might be able to figure out the difference between the height of the two tire and rim combos, and that would tell me how far my call will be either raised or dropped from the stock ride height. Is there an easier way to do this or is it safe to say 17" tires and rims are taller then a stock 64 darts tire and rim?

Also, I have a convertible, which i think may have normally had an extra leaf in the springs, do i need to get six leaf leaf springs or will 5 leaf be ok sense i want my car lower in the rear anyway? I am also wondering, should i pay the extra money and get de-arched springs or get the cheaper springs and lowering blocks?