904 vs 727?

Really? I thought the low gear set in the 904 started around 79-80ish.
And I thought that it actually was used in some of the non L/U versions too. Maybe not?

How'd they plug the L/U? As I remember it was a small added on valve module on top of the VB with a ~5/16 ish diameter "S" shaped tube that plugged into the main VB but it's been a while since I have been inside of one.