IIRC - they are identical to the current production wheel.
18" X 8", 5X110 bolt circle (common with ION RedLine/Cobalt SS/SC/and Malibu, I think). Offset either 50 or 55 mm - I can't remember.
I thought it was on the site - but actually, this is somewhat useful.
On SolsticeForum, there's an index. It is slow to update, but it is half-populated with useful active links:
http://www.solsticeforum.com/forum/showthread.php?t=2271
if you go there, search for the word "wheels", you'll get to an active link that leads here:
Wheels, Bolt Pattern, Dimensions
The dimensional data is accurate - nobody that I know of has measured a polished or a chromed SKY wheel.
The search function on either doesn't work that well, I'll be the first to admit it.