I think the main thing here is penetration. Grind out the crack in a nice "V" to acheive this. Right now you have lots of contaminents in the hairline crack, and that will cause a bad weld. If you "V" it out you can lay 2 or 3 nice beads in the joint to produce a stronger weld.
I like the idea of drilling a hole at each end of the crack. This works, I know. I would drill about a 1/8 or 3/16 hole at each end.
Awhile ago on "Trucks", they shortened a '66 long-bed frame. They sectioned the frame (which is not the same as repairing a crack) they "V"ed the outside of the joint, MIG welded from the inside, then filled the "V" on the outside, ground the inside smooth, then finished up by welding 1/4" plates on the inside. Looked good to me.
