You don't need a new K-Frame, the 67 K frame is fine. The 67 K frame is better made than the 73 up frames. I have run the 67 down K frames for 40 + years and still run the same system on my 66 Formula S. It helps to use a bearing idler arm, see below. If you get a good alignment guy, you don't need to buy a lot of the "trick" stuff. The 66 Formula S handles fine, and it has all factory Formula S suspension except the bearing idler, MOOG K7040 HD strut rod bushings, and 11/16 tie rods. In normal day to day driving it handles as good as anything.
Firmfeel Mopar Suspension and Steering