if you could maintain the correct dimensions of the lower cup and its orientation to the upper cup, and if your weld was of the full penetration design with the correct filler metal to match the axle metal and if you heat treated the whole shebang to eliminate any potential problems in the heat affected zone you might pull it off. if not, all opposing traffic would be a potential disaster! i recall one of the boys in co. that had a big knuckle housing with a few extra parts for sale. a lot of your parts from the small knuckle would fit except the knuckles. i was lucky enough to swap out my #3000 44 for the #3500 44 in a trade with bill in co. and except for the knuckles everything else should fit from your broken axle.