How long must be a four link bar?

Guy,s I have bougth a jegster four link kit but i think the bar are a litle shorter tham CEngenneering four link.
jegster has 18.5" rod to rod role.
How long it must be?
tks in advance.

Anything in the 19" range (doesnt even need to be that)...
I built this set at 19" this time... my last set were 21"...
a longer bar gives you a little bigger arc as the diff
moves up and down... but lets face it, it only moves
about 6" max(when you put it on stands with the diff
dropped)