Repair parts

Hello I'm trying to replace tandem locks for five casement windows in my house. I tried using the repair parts link but it didn't work. So my problem is that there are three different sizes of windows and different distances between the locks. The lock part numbers are all consistent, 135143. Two window locks (with the silver track in between the locks) measure at 39 15/16" (40"); another one at 29 1/2", and two windows at 41 7/16" (41 1/2"). They were measured from the top of the top lock to the bottom of the bottom lock. What part should I be using for a replacement? Pictures included.

The problem isn't the actual locking mechanism. The locking mechanisms are all the same. It's the gray bar/track in between the tandem locks that differ in length. How do I find the correct part when I only saw two lengths listed on your site?