as EVERYONE knows... my 77 sits very high..
I found a 79 that sits right, are the springs swappable onto the 77 to bring it down or am I going to need to put club sports on to get the ride height correct?

 

my 81 is riding too high too, on newish Eibachs.

I guess cutting a piece off the spring is the only way to adjust ride height on these OBs?

 

Save yourself a ton of headaches and buy a set of the lower spring perches, threaded sleeves, and adjuster nuts from an '84+ 928.
Install these, and adjust the front as you would the rear. You may also need the newer springs - I do not know the specs of the '79.
I replaced the '80 non adjustable with the '85 adjustable parts noted above (with '85 928S springs) - works great.