Hello @ranulf,
You are right, the issue is with the block not with the documentation.
To get the right input value type, please replace the mc3377xb_s32k_reg_write.mexw64 file, from the archive attached to the {Toolbox install path}\external_devices\blocks\mc3377xb.
To find the Toolbox install path, please type the mbd_find_s32k_root command in Matlab.
Hope this helps,
Marius