PAC is huge in the spring industry and has excellent products and quality. They make everything from valve springs to coilover spring for the automotive industry and springs for many other applications.
Several of the Ultra4 racers are using them. Eric Miller (KOH 2012 King) is also inhouse to help with selections. he would be familiar with both Straight axle and IFS cars. They also have a great chart for combination shock spring rates. Something to keep in the race trailer.