Is the MKIV rack any faster than the SC300? If it is then are they interchangeable?

 

Should be interchangeable they used the same rack bushings and same tie rods.

 

When I was working on a wrecked MKIV back in the day it had a busted crossmember and steering rack. The crossmember from an SC in a junkyard bolted up perfectly, however I remember I was told on SF that the steering rack wouldn't work- this was either A because of the steering column, or B because of the power steering pump. Can't remember which