Can't remember off the top of my head but if you have a multimeter you can figure it out yourself as those points are connected with pins 24A and 24B of the cart slot. Facing parts side of the board the cart slot has 2 dual rows of pins:
1A...............................50A
1B...............................50B
1A..............24A............50A
1B..............24B.............50B
24A = right
24B = left
You can solder directly to these pins.
Anyway, you'll notice that the output is very quiet with this mod so you might want to tap the signals from the headphone jack instead (and there's no difference in quality, what !Arcade! say is BS).
