4 Link Mounting brackets

I am close to making 4 Link Mounting brackets on my chassis. what is the most standard 4 link bar length? I want all of my 4-link bars to be the same length front, back, top and bottom. How far should the top link holes be ahead of the lowers to use the same length bars? I know they will very a bit on different setups but just looking for on idea, from looking at pics it looks like they are about 3" ahead of the lowers?