Thanks Floob,
I’ll give those threads a read through and see if they’ll help.

From what I’ve read so far, I need to:
1) Update the firmware on my IPAC2 from ULTIMARC website
2) Install Win IPac (for manually changing assigned keys)
3) sudo nano /opt/retropie/configs/all/retroarch.cfg
-map assigned IPac keys to reflect:

# 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.
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 =