I think the one Dan refers to requires you cut off the existing bolt leaving a stub, then you drill and tap the stub for a provided bolt and then bolt the new bolt handle to the stub of the old one.
Admittedly I have never actually seen one in person but It smacks of crap to me for a bunch of reasons. For the trouble and time I humbley suggest you get a good gunsmith to bend/forge or cut off and reweld it depending on how much length etc is available. ANd get him to drill the mount holes you need in the right places.
Not every smith likes seeing these jobs come through the door so ask around and ship the rifle to whoever has a good reputation and will take the work. Worth it to spend the money to get it done right.
OR get a home gunsmithing book, a torch and a drill press and do it yourself. (Don't use an expensive gun)