The factory style ejector to extractor conversion is in the FAQs also, I do the hybrid version that extracts unless it sticks, then it will eject, it uses the ejector claw with an extractor cam and a short spring in between to account for the difference in length, plus an extractor leaf spring, the ejector has to be modified too, that's what Pete has on his 445SM, it can be done at home if you have a drill press (or mill of course). The only way to know if H&R will work on it is to call them and ask, they've fitted second hand barrels before, it probably has a bad chamber which may be able to be cleaned up.
Tim