I received my new HD Bilsteins for the rear today and will be installing as soon as I remove the motor - several questions:

1) How do I know if I have the stock springs, or heavier ones? I am assuming stock - they are black.

2) Which notch do I put the spring perch on? At least a starting point? It appears to have ~5-6 notches.

Most 914 rear springs are black....at least the ones that fit on stock style perches.
As far as knowing if you have stock springs or not currently....
1)When you remove the shock/spring combination from the car, if the shock is fully extended and there is still tension on the spring ( still slighly compressed) then you have stock length springs. If when you remove the shock/spring combination there is slack ( shock is fully extended and spring is easily moved up and down, IE loose) then you have some aftermarket springs. They could be 100#, 140# or 180#.

2) depending on what length springs you have and the ride height you want, will indicate which notch you use on the shock.

the "free" length of stock spring is I think 18"....that is if it has not been cut, then again, it wouldn't be stock

best bet is to remove springs and measure them....the amount of pounds it takes to compress them 1" is what the spring rate is....

Anything up to 140's will still have a little tension on them in the stock perches.