NEF never replaced H&R...
I disagree. The "original" H&R company changed hands several times. The one owned by the Rowe family that existed in the 1980's slowly went out of business and closed up circa 1986. James Garrison bought the remains of H&R in 1990 and renamed the company H&R 1871. This successor company made mostly products of the same design as those made under the previous H&R firm owned by the Rowes.
As we know, in 2000 Marlin bought H&R 1871; subsequently Remington bought Marlin in 2007. I seem to remember that manufacture of the centerfire revolvers stopped under NEF but these were essentially the same basic design of pre-1986. I believe the last revolvers made by NEF were blank-firing starter guns and these were in the catalog after the centerfire revolvers were dropped. Remington killed the NEF brand entirely when they acquired the company.
As to any commonality of parts between pre 1986 H&R and NEF revolvers. Of course H&R pre-1986 would change their designs from time to time. The NEF revolvers were basically unchanged during their life cycle at H&R 1871. But I've looked at the parts lists at Numrich and there are a number of internal parts that have the same numbers between the late H&R product and the NEF revolvers. Like hammer, trigger, sear, etc.
There is a book about H&R revolvers by Bill Goforth (very expensive) but it doesn't cover anything after 1986, nothing on NEF.
I know a bit about these developments. I've got some pre-1986 H&R's and NEF single barrel shotguns and rifles. The company of the moment used to sell a product line of accessory barrels. If you had the appropriate frame, you could buy quite a number of different shotgun and centerfire barrels in different gauges and calibers. Every time the factory would change hands, the process for obtaining these would change. So you had to stay on top of that. Some of these rifle barrels, depending upon caliber, have become quite valuable for what they are. Remington wasn't interested in continuing this business. The version of the company that made NEF products was fairly successful and the owner made good money when he sold out to Marlin. It's only my impression, but I think when the Freedom Group (Remington's parent) bought Marlin, they kind of got H&R 1871 by accident; part of a package deal thing. Once acquired, they didn't know what to do with it so it lingered and eventually they let it die. At one time, there was a surprising following of NEF single shot hunters and shooters. In the recent Remington bankruptcy sale, I seem to recall that the H&R 1871 assets were sold separately from Marlin but I don't remember who got them. Time will tell if anything comes of this.