Total advance is not determined by the springs, only the point at which the mechanical advance begins.

There is a pin with a bushing on the bottom side of the plate with the weights. You can experiment with a thinner bushing, or no bushing, to increase the total mechanical advance.

The easiest way to remove the bushing without risk of dropping it is to pull the distributor and drive the pin out of the drive gear, supporting the drive gear on a padded block. Slide the shaft up and out, remove your weights and clean them up by rubbing the bottom side on a sheet of wet/dry sandpaper until smooth. Remove the bushing or replace the bushing on the advance limiter pin, then reassemble.