Well Bill, I'm a retired engineer too and when I was replacing the bolts on mine I did cut down some grade 8 ones to keep the shank in the joint. I didn't bother to calculate the shear strength etc but noted that the ones I removed were fully threaded and showed some deformation in the joint area so considering the small cost in money and time I figured it was worthwhile to do what I did. I've seen what happens to cars when the U joints fail and it can be ugly. BTW, I was removing my tranny to get to the clutch as the relief arms or whatever they are called were coming loose causing it to drag when it shouldn't have! Sure shifts well now.