Except there are quite a few people that run the 73+ spindles and brakes on '72 and earlier cars. The usual interference point with the '67-'72 sway bar is the caliper if you try to put the caliper to the front, and that has been covered here many times. The interference at the ball joint is not nearly as common an issue. Yes, the factory welds varied wildly in quality, so it may be that those are factory arms. The pictures from the OP aren't great, but again, it looks like the tabs are in a slightly different position than many of the ones I've seen. It doesn't take much, and I don't think the interference in this case is a major issue. They're 50+ years old, so they may have been tweaked or damaged at some point too.
Using a '73+ sway bar is not at all an option unless you change out the entire K frame and move the tabs. Not at all the best way to fix the issue.
It's definitely hard to tell what's going on with the OP's LCA's based on the supplied pictures, for sure. The factory tabs have a lot of bends/angles and look quite different from different angles.
Nonetheless, the OP isn't anywhere near the only person to have done this swap and that's not the "usual" interference point. The hardware in the OP's picture definitely looks like part of the issue, the bolt is too long (it's a standard grade 8) and the nut on the back is very thick. And I don't think he's losing a ton of motion, so a slightly shorter bolt/thinner nut would probably be more than enough.
DoctorDiff sells these bolts with a different style nut, and if I remember correctly the "standard" grade 8 size you'd be able to get at the hardware store is too long, I think he orders a length that's an 1/8" or 1/4" shorter than the typical hardware store selection
Mopar A/B/E Body 5/8" Lower Ball Joint Bolts and Nuts
