The 9018 is plain old 9018 stick welding rod. I didn't develope the procedure, so I don't know what else they might have tried over the years, but this is what worked. There are "Tool & Die" rods that give a tool steel deposit made just for this type of work, they are what You put on the working surfaces to give heat and wear resistance. If You tried to use the tool steel rod for the entire repair it would be too likely to crack completely apart, the 9018 allows some "give". The steels I mentioned should not be heated above 400 f because that would make them softer than they are supposed to be [draw the temper too far]. The material You are working with could probably be heated to 900-1000 f without a problem, and being high speed steel of some kind that would probably be a better temp for pre and post weld heating, but We really should know the particular tool steel alloy to get the best information. My best guess would be to hold at 1000 f for 1 hour after welding. How You are going to do that without a furnace I have no idea. For an amaturish job You might tack it together with the 9018, heat it to black with the torch, do Your welding, grind off the scale and tops of the beads so You can see the oxide colors, heat it to black again and then wrap it up in fiberglass insulation to cool slowly. DO NOT UNDER ANY CIRCUMSTANCES COOL THIS PART WITH WATER.
After the weld repair the mounting surfaces will need to be ground flat on a surface grinder, and the working surfaces need to be ground to the proper contour and size. Dowl pin holes on each side of the repair will not be in the same relationship, etc. If they don't have an in house toolroom they may not be able to use the part even if You do weld it together, find out first.