Use the basic spring perches $20 and ditch the G.M. spring perch design that's used with the rubber insulators. If you're throwing any amount of power at this you don't want to use the rubber insulators. We tried polyurthane insulators on my Son's multileaf setup and also cracked them, so now he is running with no insulators and we added a steel spacer to the spring pack to make up the thickness difference-rearend is solid mounted on the springs with no rubber etc... and it works great. Also use two U bolts and get rid of the T-bolts!!