idunnomrroboto.... the arm is key'd to the shaft, the weld is to hold it on... all rotational Tq load is still transfered through the key'd part its just welded onto the shaft, it would be an ok repair however there would be a risk of damaging the trans range switch but wrapping it with a wet rag while welding and a slow trickle of water after welding should keep the heat from transfering into the plastic switch arm inside the housing.
the problem is the best current path to weld it would be grounded directly through the shaft from the bottom, so that would mean your happy ass would have to drop the pan here. on the plus side after a drive from up there in the sticks it wouldnt be a bad time to change out the fluid and filter (get a good wix or transtar filter, none of those chink filters)
i could probably drill n tap the shaft for an M8 bolt but that would be a possibility but we may have to yank out the brake booster and swiing the master cylinder outta the way
btw all them a's i edited out were cause my microsoft keyboard died