I have done a few mauser bolt handles - cut partially through the root about 1/4" or so from the bolt body, heat red and bend the handle down, then fill with weld. Make another partial cut lower down on inside of bolt handle shaft - heat red, bend out and fill with weld. Grind and polish. The two cut / bend / weld add a bit of needed length to the bolt handle. Have never started with a "bent" one - only worked on straight handles. Generally want the bolt handle to "stop" rotation on solid contact of the bolt handle root with the receiver ledge, and not touching the wood of the stock, at all. As mentioned above - might need to be "clocked" - that safety notch partial circle needs to be exactly in line with the groove in the rear bridge - Top Dead Centre.
So far as I know, the first heat treat area to be concerned about is the cocking cam surface at the rear of the bolt - if it softens, then it can gall and bind up against the cocking piece cam face. For that job I always have a heat sink screwed into rear of bolt, heat control paste slathered all over, and bolt body in a pair of forging blocks as much as possible for welding - they are also a great heat sink. If you start with shiny polished steel surfaces, the heat colors will tell you how hot you were - straw gold/yellow is up to 450 degrees F, browns and purple are mid to high 500 degree F, dark blue you are pushing 600 degree F and that is getting into annealing (softening) temperatures. Using heat sinks and heat control paste, the colour does not get to the bolt body at all. You would have to get the whole thing stupidly hot to be taking out the hardness all the way up at the bolt lugs, by welding on the bolt handle. I do not think the bolt body, between the cocking cam and the lugs, is hardened at all.