The difference is the length from the bottom to the spring seat. I put gtst shocks in the stagea first time around and wondered why it lifted the front. Then we decided to actually take a look at what we pulled out, and hey presto, we found the problem. Other than that, that is all that is different.
Sorry couldn't tell you the spring rates, I think they are the same as 33 GTR, cause the front springs are lowered 30mm heavy duty Kings, and I got Kings to make a set for the rear to match, but they are a little softer than the front and in my opinion, need to be a little stiffer.
If you rang Kings and ask them they might remember, it was only a couple of months ago that they made them.
Cheers
Gary