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

My Duster is getting down right scary on the freeway!

Then i realized this same suspension was holding a slant 6 for 38 years of its life and is now carrying a 360.

Now... I just kept the /6 K frame and used the V-8 adapter. When I look for a suspension kit, should I be looking for a /6 suspension kit if thats all that is going to fit due to the K frame?

If it's all the same, what is suggested I get? A performance kit of some kind?

I found this one...

http://www.justsuspension.com/mopar-a-body-front-end-kit-73-76-disc.html

or then there is this one that cost more...

http://www.p-s-t.com/s.nl/it.A/id.170/.f?sc=12

Thanks Much!