Front end wont stay aligned

Having problems with our 67 Barracuda not keeping an alignment. Everything up front is brand new:
Upper/lower ball joints
Tie rod ends
sway bar links
tires (radials)
Upper/lower control arm bushings
new eccentrics
My dad and I have lined this car up at least 10 times. When we are finished, it looks great, and handles great, but about a 1/4 mile down the road....it goes bat **** crazy.Every single time. I have recently heard of these k frames cracking around where the lower control arm bolts through. Is this common?
This is not my first mopar, and my dad has been doing alignments for 30+ years. Just don't know what to try next. Any help would be appreciated!