My new mods will go with option to set in the .ini file the keys that will be used with XBox 360 control, so, based on the list below you can choose the right number to use:
BACK = 13
START = 12
X = 14
Y = 15
A = 16
B = 17
DPAD UP = 8
DPAD LEFT = 10
DPAD RIGHT = 11
TRIGGER LEFT = 5
TRIGGER RIGHT = 7
BUMPER LEFT = 4
BUMPER RIGHT = 6
STICK LEFT = 18
STICK RIGHT = 19
The .ini file will have same base name of the script and will be located in the gta Scripts folder, after changing the keys you must enter the scripthook command reloadscripts or load a saved game.