08 Mastersbuilt rear end setting

I have a 08 Mastersbuilt. The set up book calls for a 18 3/8" or 21" J-bar. Assuming I have the correct brackets, this will pull the rear end too far to the left. Is there a measurement from the rear end to the frame that I can check to see if it is correct. This also has the 4 bars at an angle. But may have to move birdcages.

We run 15 3/4 from inside of 90/10 plate to center of RR frame rail. Birdcages are 7.5” from inside of rotor to centerline of lower shock mount