I installed the Cobra Valley QA1 shock and spring kit on my SPF shortly after they were released. I upgraded from a set of very worn out AVO's and what an improvement!
The Cobra Valley setup is custom valved for the SPF MKIII, and have custom made bushings that allow you to use the original bolts. No changes need to be made to the frame or arms - they bolt on perfectly.
Here is a link to the shock and spring upgrade
Cobra Valley's SHOCK & SPRING Suspension UPGRADE
I went with the 350lb springs front and rear. This, along with the upgraded suspension mount kit (a
MUST-HAVE in my opinion) was the best upgrade I made to my SPF, and I have made many upgrades over the years!
Here is a link to the upgraded mount kit
Cobra Valley's SUPERFORMANCE Rear Suspension Mount UPGRADE
Hope this helps,
Jim