When i had a pump gas 408 in the car i used the silver and the lite blue spring together. Think the initial timing was about 20*. Depending on how big your cam is, you may be able to just lock out the timing. I tried both ways and couldn't tell much difference. If your cam is 270*@50 or larger on intake, I would just lock it out 34*-36* should work fine. You may need a start retard when locked out.