Tap in back into place Freaky. Once you're sure that it's in the right spot and everything is lined up grind a vee in the crack with a die grinder to get decent penetration and then get someone competent to TIG weld it up. They will need to go past the end of the crack at either end, but a good welder will know that anyway. It's only on the engine mount support tube, so it will be fine. Whatever you do, don't get it brazed.
Pete.