if you read the code above what you just posted it read’s this

# Keyboard input. Will recognize letters ("a" to "z") and the following special keys (where "kp_"
# is for keypad keys):
#
#   left, right, up, down, enter, kp_enter, tab, insert, del, end, home,
#   rshift, shift, ctrl, alt, space, escape, add, subtract, kp_plus, kp_minus,
#   f1, f2, f3, f4, f5, f6, f7, f8, f9, f10, f11, f12,
#   num0, num1, num2, num3, num4, num5, num6, num7, num8, num9, pageup, pagedown,
#   keypad0, keypad1, keypad2, keypad3, keypad4, keypad5, keypad6, keypad7, keypad8, keypad9,
#   period, capslock, numlock, backspace, multiply, divide, print_screen, scroll_lock,
#   tilde, backquote, pause, quote, comma, minus, slash, semicolon, equals, leftbracket,
#   backslash, rightbracket, kp_period, kp_equals, rctrl, ralt
#
# Keyboard input, Joypad and Joyaxis will all obey the "nul" bind, which disables the bind completely, 
# rather than relying on a default.

it doesn’t reference any “lshift” “lalt” or “lctrl”

it’s only reference is “ralt” or “alt”

so the lines should look like this with no space.

# rather than relying on a default.
input_player1_a = ctrl
input_player1_b = alt
input_player1_y = shift
input_player1_x = space
input_player1_start = num1
input_player1_select = num5
input_player1_l = z
input_player1_r = x
input_player1_left = left
input_player1_right = right
input_player1_up = up
input_player1_down = down
input_player2_a = a
input_player2_b = s
input_player2_y = q
input_player2_x = w
input_player2_start = num2
input_player2_select = num6
input_player2_l = i
input_player2_r = k
input_player2_left = d
input_player2_right = g
input_player2_up = r
input_player2_down = f
# input_player1_l2 =
# input_player1_r2 =
# input_player1_l3 =
# input_player1_r3 =

i included the lines with the “#” in order to help you with placement.
the I-PAC was built for MAME and i think MAME Default controls anywise overwrite Emulation Station. i also included start and slect as palyer and coin buttons for each.

and here is my huge post about the I-PAC.

How to key map mapping the keyboard for the I-PAC or other keyboard duplicator.