[Rick Parker]

The bushing is to either extend or limit the total amout or number of degrees of timing the distributor will permit. The springs used probably slow down the rate of advance. MSD included the set of springs and bushings with their new distributors. The spring & bushing kit is available separately for $12-$15. There is a chart included that shows exactly what each bushing or set of spings does to the advance rate and at what RPM. It is very easy to change out the parts.

PS: If the specific changes (color of bushing and which springs) that Rousch are using could be determined, the changes could be made in the field very easily by the end user.