Hey Lanse, looks like it's about time you learned to braze. In a situation like you'v got here a 7018 simply isn't going to work. I can say that because I've tried it before and the result has always been the weld pulling away from the cast, or the casting simply breaking off right beside (within 1/16 inch) of the weld due to the change in chemistry in the cast caused by the weld.
That said when it comes to a good, cheap, and lasting repair for cast you simply can't beat torch brazing. Over the years I've repaired parts of vices, tractor axel housings, flywheel housings, etc, etc, all by torch brazing. I've also watched an old welder/machinist, that was my 'go to guy' for anything welding related til he passed away a couple of yars ago, braze the head off of a pretty good sized old hydraulic press. In that instance parts of the casting were well over an inch thick. What he did, and what I always do myself, is to V the cracked area either halfway through from each side, or all the way through from one side (depending on the part). From there get everything hot and then start brazing. Once your done put the part in a bucket of sand to let it cool slowly, just as you would if you were to weld it. In the end you'll have a repair that should be just as strong as the solid cast part origionally was.
Beyond that, good luck, that's too good of an old vice to just throw away based on an easily repairable break.