The original H&R went bankrupt in 1986, H&R1871 and NEF bought them out of bankruptcy and have been making firearms in the same plant in Gardner MA until last fall when Remington closed the Gardner plant and moved production to Ilion NY. The original pre''87 H&R firearms were all made on cast iron frames, H&R1871 and NEF frames are different, using cast iron for shotgun(
SB1), heat treated investment cast alloy for rifles(
SB2)(until last year when they changed and offered 357 and 44mags on the cast iron frame. Those older pre-'87 frames apparently aren't made to the same tolerance as modern frames so some older barrels will fit, some won't, some also had a different forend fastener. Fast forward to 2009, there is no NEF now except for the imported shotguns and the starter(blank) pistols, everything is now marked H&R, single shot rifles have been for the last year or so. Traditionally Handirifles were NEF, Ultras were H&R, but that's no longer the case, all are H&R.
Basically, the only way to know if an older, or any barrel for that matter, will fit a modern frame or can be made to fit, is to try it.
Tim