If you want to rechamber to K-hornet, you can do that by hand with the proper reamer, just stop when the reamer touches the rim cut in the barrel.
Anything larger like 221 or 222 should be set up in a lathe, you will surely get an out of round or crooked chamber if you do it by hand. The hardest part is getting the bore (not the outside of the barrel) perfectly centered in the lathe. Then it's a matter of stopping when the headspace is correct (I believe there is a 0.004" difference between the go and no-go chamber headspace gages, so very soon after the go gage will fit, you will have gone too far and the no-go will drop in.
The only way I know of to salvage a no-go chamber is to rechamber to a longer cartridge like 223 or shim your reloading dies to make slightly longer cartridges to fit the nonstandard chamber.
The extractor is the easy part, just buy a 223 extractor from Brownell's. H&R might sell you the extractor also.
