I have worked with NEF/H&R rifles and shotguns for more than 30 years... I have done a couple hundred builds and swap barrel sets... I don't recommend that you bother with investing in a rechamber of a Sportster rimfire... they are much cheaper to find in excellent used/factory chambered condition... the centerfire rifles are another story all-together and are and excellent platform for experimentation... I have done rechambers, rebores, and stubs in dozens of unobtainable cartridges... I had an aweful lot of fun with the platform for a long time, but have since downsized and do very little with them anymore, since the product line was discontinued. I do have dozens of pictures, and many CGNer's are still hunting with these rifles.
BTW, both Choate and Boyd's make stocks for the Sportsters and SB2 rifles...