It can be welded, but not easily. Body is correct, welding 40 year old cast aluminum is hard enough, but oil-soaked cast aluminum is the Devil’s Balls.
To weld it properly, split the cases, parts wash the cases at a machine shop. Then clean them some more with Acetone, inside and out. The surface area needs to be scrubbed with stainless brushes, and I use 4047 filler wire for cast ally and peen the weld as I go. Else, you will get tons of porosity that will produce seepage.
Someone proposed cutting off the bosses and edging those back on. I wouldn’t unless absolutely mandatory. Even then, I’d have donor bosses available. The bosses are thick, the cases not so much. You’d need to grind bevels into the boss mating surface to get sufficient strength and penetration and use multiple passes, peening as you go.
Welding aluminum is so difficult. Welding cast is tricky. Welding 40 year old cast is a whole other bailiwick. And the oil and grime saturation, and a competent welder who will insure it’s right will charge you by the hour, and expect it to be 3-4 hours if you clean it first.
Now you may get lucky and there’s a defined crack inside the case, and it can be ground out and grooved, filled, then filed. That might take an hour. But expect the worst, and pray for the best. With cast ally, the heat from welding causes the air pockets in the surrounding area to expand. You end up with “blisters” and those are weakened. So it takes some care not to cause more damage than repair.
I’m not trying to say it’s impractical or impossible. Just explaining how it should be done correctly so you know ahead of time what to expect. If you’re splitting the cases over the winter anyway, get it done. If not, use some donor cases then keep track of the bearing shells.