No 4low?
I have a '75 with twin sticks. I also left the pills in place.
To go into 4high - place the drive stick in 2 (rear wheel) high first, THEN go to the front wheel control (Right stick) and pull it back. You might need to feather the chutch a little to unbind the gears. Both sticks will be in the rear position.
To go back to 2 high, move the front wheel drive lever to neutral
To go into 2 low (rear wheel only) move the left lever forward into neutral, then forward into low.
To add the front the wheel to the drive system move the right lever forward. When in 4wd, both sticks will be forward
To go into rear wheel low, move the right lever to the neutral position
To go to rear wheel high move only the left lever to neutral then back one more slot to high. Your left lever (the rear wheel control stick) will be to the rear, the Right lever (the front wheel control stick) will be in the middle or neutral position.