Help! Crack in frame?

[vanderbilt]

I was fixing a coolant leak in my 70 and to my horror noticed a crack in the frame around one of the unused motor mount holes on the passenger side, top of the rail. I bought the truck about six months ago and can't believe I didn't see this. The question is how do I fix it? I have a mig welder... Can I just run a bead on it or is this something that will require some professional attention? I've tried to attach some photos and would appreciate any advice...
Posted via Mobile Device
Posted via Mobile Device
Posted via Mobile Device