The wheels should be 18x8.5 +45 and 18x10 +53. Weights will be approximately 21 and 22 lbs. Hope this helps.
By the way, these offsets would work on a 996 without issue.

 

This what we call 'ask an expert' because I had no idea. All I knew was the widths and diameters, model designation, and that they fit my 993 nb perfectly.
Confronted with questions about offset, weight, and 'will they fit my car?' I was lost.
Luckily the good folks at Forgeline volunteered to contact the original owner and check the build records .
And here you have it.
A big thank you to Dave at Forgeline. Not only builders of great wheels but providers of over the top service.

 

If I like the other 18's on track maybe I'll pick these up from you.

 

now...if that^^^^don't put a smile on your face, make you feel good about this place(rennlist), I don't know what would.

Good Porsche Karma credit all round

GLWS

 

I can't speak for Rick, but how they might fit on a Cayman is something I would like to know as well. Option XRR OEM Cayman wheels were the same widths (8.5 and 10") and I believe they had offsets of ET55 and ET42, respectively. If these are +45 and +53, they are about 10mm less offset in the front, and 11mm more offset in the rear. A 10mm spacer would get the rears to fit a Cayman well (with longer bolts or studs), but the fronts would probably be a close fit to the fender lip with the stock 235 width tire and might require rolling the lip. Many folks run a 5mm spacer without any interference on the Cayman, but that is with stock 8" ET57 rims. These are 1/2" wider with 12mm less offset than the 8s, so you would be pushing them out about 19mm total compared to stock. You might be limited to running only the stock width tire and not be able to run any wider fronts, like the 245 or 255s that a lot of people prefer.

YMMV, as there is a lot of variation among different tire manufacturers when specifying width, and tread shoulder profiles also vary (rounded vs. square) as well.
TT