Hi John. The best way to get ahold of Bryan is to e-mail him direct at
bbmfg@jscomm.net
I've been installing a lot of Carrera coilovers lately, and on big blocks we use 525 lb. springs on the front. It's possible you may need the 2" spacer between the adjusting collar and spring. But so far I've only had to use them on a couple of cars. We've been using 185 lb. on the rears. If you are using RCC, the rears are 170 lb. Right now I can't remember the front rates, so you need to contact Bryan.
Ron