what size 4link do i get?

i want to order a 4link from suicidedoors.com but i dont know what size 4link to get. it says when i call to order i need to have measurements. i wanna run 2 bars forward and 2 bars back. i wanna cut off my leaf hangers, i dont wanna mount them on those. so what size should i get? how do i measure it and what size do u guys have? keep in mind i dont want to relocate my gastank. (thats why im gonna run 2 reverse, only way i think?) thanks in advance