Can see horizontal crack, can't see if there is a vertical crack because the lighting is shadowed. Probably is a vertical crack. What I see is no problem for welding. Good fillet bead, no grinding. If a person had no welder available, you could possibly put one or two socket head cap screws thru member and frame. Under the crack, 1/4-20.
As Grigg said, welding on the frame is to be avoided. Stay on the cross member. You don't need a mega weld. Forget what I said about drilling a hole at crack ends/grooving/pulling. Good you gave us a pic, it did sound way worse.
As said, it lasted a long time thru endless vibration and twist. If there is more to it than those cracks at one rivet/cross member ear, each side of truck, point it out. Those ain't nothin.
