EDIT: Hold on this info... there appears to be a conflict as the Granite BLX storry board also says the Granite uses the LWB chassis but the parts info shows SWB for the Granite (all models). I'm trying to find a confirmation of the battery tray measurements for the SWB and LWB chassis.
=============================================================
Granite MEGA, BLS and BLX all share the short wheelbase SWB chassis.
The Official Arrma Granite BLX story board has the following measurements posted:
Battery Tray takes maximum sizes of 157x48x27 (LxWxH in mm)