Slight frame crack. Opinions?

Sort of common place to crack. I've really only heard of A-bodies cracking in that area. Both my 68's had cracks there and I looked at some other A-body in the junkyard years ago and found some with similar cracking. My 68 Dart convertible only has some small cracks.

They can also crack on the bottom of the frame rail under the K-member pads where the K-member bolts to the frame. Not as common. Check that area real close if you don't take the K-member out to see if you can see stuff from the sides.