Which longacre for bump steer

What is it that you're noticing that you're attributing to bump steer? Because most of these old Mopars aren't actually all that bad with regard to bump steer. So, what you're noticing and attributing to bump steer could be something else.

While this article is about using FMJ spindles, it does a pretty good job of explaining what bump steer is and how it effects handling on the street. It also provides an analysis of both A body and FMJ spindles with regard to bump steer, and you can see that for a street car the numbers aren't bad at all. I mean, they're not race car numbers, but they're not bad. They also cover some of their method for measuring everything if you click through the pictures and captions.

Swapping Disc-Brake Spindles - Mopar Muscle Magazine