Check the specs for pen length here, by clicking on the Specifications Tab.
https://www.bereahardwoods.com/pen-kit/sets/sierra-vista-platinum.html
Stated pen length is 5 1/8". . If you want to go longer, you will have to replace the brass tube with a longer tube.
Your present tube length supplied with the Sierra Vista is 2.21" long.
That means going to a brass tube meant for a Sierra Click pen, which has a tube that is 2.42" long.
To go any longer than that, you will have to buy some 10" long brass tubes (27/64" diam. so-called) and cut one.
The only vendor who stocks long tubes of that size is Wood-N-Whimsies.com. . Trust me, I have looked for them.
I have a finished pen in my hands and I can lengthen it to 5 3/8" and have the twist still working. . I would not attempt to go over that. . You would not be able to go over 5 7/16" for sure and still have the cap engage with the twist mechanism.
5 1/2" is definitely too long.
Why do you want to go that long, if you don't mind me asking ?