This is a follow up in case anyone's interested in knowing the length of the Ground Control PL510 (not wagon) rear coilovers. I say this as I had previously contacted Ground Control by email asking what the unsprung length was so I could figure out if I would be able to use them in my application... I never received a response.
Here's a reference pic of the coilovers:
The length is 21 3/4" from the center of the bottom mount hole to the top mount point (bushing). Though I'll have to see when fitting, but it seems like this is going to be a tight tolerance to fit for what I need. Since it appears to be slightly shorter than the stock ones and I'm not sure how it'll sit yet. But if need be, the top stud has enough length that I can add some shims to get some more height to the coilover's unsprung length.