How to soften them up for the street? I have the shocks on stock 914 springs also.

You can send them to Bilstein in SoCal and have them re-valved. No other options I know of.

Or you can buy Koni's and adjust on the fly.

Just break em in for a couple of decades I'm sure they will soften right up

I went with the sport model for my car. I won't know how they feel for several more months when I actually get to drive it.

You would obviously have the spring perch on the lowest compression setting?
Billys are known to have a firm ride as opposed to others what ever they are fitted on but it sounds like yours are firm,are you following the bumps or just bouncing over them?

Have included pic of mine to show how adjustment sets in the notches on the shock body,presume yours are the same,cheers

Click to view attachment

What size (#) rear springs do you have. They make a difference!

There is no lowest spring compression setting. The groves set ride height only. If you notice a difference in stiffness it's due to suspension dynamics changing because you are moving the weight bias to the front or rear by changing rear elevation.

the car rides on the springs the shocks control the springs ..your springs are to stiff ..then again probably just seems that way becaus ethe old shocks were shot ..like new shoes there a
little snug at first..

Stock 914 springs as described.