I just sent Phil an email reply with several pics showing the construction/installation of the Russell backrest on my ex-NT. Then I logged in here. If Phil wants to post my pics here, the combination of my pics and Woodaddict's pics will give you a complete overview of how Russell makes an NT backrest work (if Russell hasn't changed the way they do it). Although my NT was destroyed in the accident, my Russell seat did not get damaged (go figure) and I kept it in case I might buy another NT after I recovered from my neck surgery (it wasn't back surgery as Phil stated). The surgery was a success (for the most part), but after an 18-month recovery before my neurosurgeon said , "Yes, you can ride again", I didn't feel comfortable doing 2-wheels anymore (some limited neck motion and vertical balance concerns, etc) so I bought my 3-wheel Spyder 2 years ago and offered my NT Russell seat for sale here on the forum. Someone on the east coast bought it, but I don't remember who it was ("Jim"?...I can't find my correspondence about it with whoever bought it). The pics I sent Phil are some of the pics I sent them at the time so they could decide if they wanted to buy it.
Yes, you insert the bottom bar portion of the backrest into the pax portion of the seat in an (almost) horizontal ("parallel") direction. Then the backrest swivels up/down using a "hinge" that is also located on the support bar attached to the backrest itself. It's rock-solid construction and installing/removing the entire backrest takes only a few seconds. For me it was the best "farkle money" I ever spent for my NT. I liked it so much the first thing I did with my new Spyder was ride it to Russell in California and have them put a $1500 Russell seat on my Spyder (the Spyder Russell seat is quite a bit larger, hence the higher price, just like one you might buy for a Gold Wing).