Barry, as stated above, you have to make sure that the large pin is fully retracted like it is HERE
The small pin on top is heavily spring loaded and you won't be able to move it. If you have the pin retracted like that, you can tap that little pin to make sure it is working. If it is, strike the pin directly on top with a hammer and it should release the other one, which will shoot out about 3/4" to lock it into the frame rail.
You'll never be able to push that little pin in though on your own. Assuming it works correctly, just twist the lock to retract the big pin again and quickly shove it upwards into the receiver in the bottom of the frame rail on the LR3/4. That little pin should hit something in the Frame Rail that causes it to fire the large pin into place.
FWIW, the new style is nicer looking, but I think the older one gives a better departure angle if you take it off road with that in place (not recommended).