Don't know about the Griz Flatshooter, but the Super Kodiak...they didn't list a brace height in the literature.
They just listed a shooting clearance height/Strung height. It's 61" for the 64" AMO Super I have and 57" for the 60" Super Kodiak. That's 3" less than the AMO number for either version.
For my 64", that worked out to be a 8 1/4" brace height. May need to tweak it some for yours to reduce hand shock and noise. But that will get you close.
Hope that helps!
How long and what weight is your Super Kodiak?