F,M, J- body K-frames were used for a lot of street rods prior to more convenient alternatives that are seen today. They had been used under late 40'5 and 50's era mopars to get disk brakes up front and some people like a torsion bar suspension.

But today there are Dakotas which have a rack and pinion steering and can be adapted to some of these trucks easier. As those F,M,J body cars get older parts get more expensive which makes them less desirable swaps.

The other answer is something fitting may have more to do with the tools you have at hand and your ability to make something fit. A persons ability to fabricate is often defines the limit of what "fits" and what doesn't when it comes to street rods.

Brian