Fortunately it appears they didn't weld on the spring leaves, just the axle housing. If they had welded on the spring leaves, I would consider them scrap. Useful only for knifemaking stock. Everything else can be salvaged. If they were carrying heavy loads, I would check the axle housing for straightness.
I had a '72 Chevy 1/2 ton that had been used to carry a monster slide-in camper and had a sagged axle. I had it straightened, but they got the center section out of line with the axle tubes, even though it was straight at the wheel ends. It had a limited slip in it and the binding of the side gears shucked the petals off of the friction plates and threw the bits into the pinion bearing. I wound up replacing the entire rear axle. Of course the guy I bought it from neglected to mention the damage.
I happened to see him at a campsite a year or so later, and he looked incredulous that the truck was still on the road.