Rear leaf help

[Never Satisfied]

I just got a 1975 Jimmy not too long ago and it's 100% original. I'm putting a 4" lift on it and have no idea how to tell if I need 52" or 56" rear springs. The guy used it to tow and the rear springs are flat (no arch at all). How do I know what I have?

 

[obijuan]

measure from eye to eye but do it along the main leaf of the spring. likely they are 52's.

 

[Never Satisfied]

Ok, they're 52's....thanks.