[HO455]

Personally I would be concerned with cracks starting in the spots with red arrows and possibly at the yellow arrow too. The photo makes it had to tell if the spot at the yellow arrow has any sharp corners. The mechanic had the rights idea when he drilled the hole at the front end but lost it in execution. Those 2 cuts from the saw blade in the drilled spot are prime places for cracks to start.

And if it was my truck I would weld in a patch piece similar to the green out line in the second photo. The PO of my Burban cut the frame but with a torch which didn't leave any sharp corners. I only had to grind the slag off and make sure there were no sharp corners for cracks to start. Without measuring I don't believe the cutout in my Burban's frame is as deep into the Cee of the frame as yours is, but it is close.