Are suspension parts differernt for a V-8 K frame and the slant 6 K frame?

For a disk brake car those kits are identical for a /6 or V8 car. All the bushings and ball joints are the same from /6 to V8, the only difference in the front rebuild kits is because of the type of brakes, which vary by year. As far as which kit to get, it looks like the PST kit is more because it includes an idler arm, cam bolts, and sway bar end links.

If you switched to a V8 though you should upgrade your torsion bars, which are different for a /6. Get a nice set of 1" bars from Just Suspension, Firm Feel or PST. The /6 bars are ridiculously soft, upgrading the bars will give you a much better handling car. But other than the torsion bars, everything else is the same.

I would also suggest getting a set of offset upper control arm bushings, Moog 7103. The offset bushings allow you to set the alignment of the car for modern radial tires, ie, with more + caster. Below is an alignment guide and the install instructions for the Moog 7103's, which is different than the "stock" instructions that come with them.