How to fix a cracked frame?

[Brian L]

I have found some cracks in the frame on my 88, 1500. The small diagonal crossmember next to the spare tire is cracked almost all the way through, and then the curvy crossmember that holds the tire is cracked about two inches on the bottom where the two meet.
Also there is a crack at least 6 inches long on the bottom of the frame under the driver side door, and another one maybe 4 inches long on the side above it. It is right before the frame starts to curve up towards the engine. There is a big dent on the bottom of the frame that almost looks like this corner of the truck was driven off a brick wall or something. But the guy I bought this truck from was a drunk so I wouldn't be surprised.
I asked my welding instuctor about maybe welding these cracks up. He said not to weld a frame because it would change the temper of the metal, and possibly sag it making it even weaker than it was before. He also said with the amount of scale and rust on the frame that you would have to grind a lot of it down to make it clean enough to get a weld to stick on also making it thinner and weaker than before. This frame is very rusty, and there is lots of scale peeling off. Instead of welding he recommended drilling some holes in the frame and bolting in a piece of angle iron over the cracks. I think what he said makes a lot of sense, but I just want a second opinion. What do you guys think about this?