I have a 2008 Giant Reign X1. The bottom bracket has developed play again (race face dh x type bottom bracket). I have a set of truvativ holzfeller OCT cranks that i want to install but will require me to use a Truvativ Howitzer XR bottom bracket.

I have located the bb but I'm stuck on which one to order. There's two.

68/73 x 51mm

or

68/73 x 56mm

Which is the correct one for the 08 reign x? Is there a way I could measure and if so what is the proper way to measure? is it center to middle of the dual rings? Do i take into the account that there is a spacer in between the drive side cup and the bottom bracket shell and subtract?

When i purchased the raceface dh x type bottom bracket, it was simple. I just purchased the 68/73 and it came with spacers. These truvativ ones are confusing me.