I've picked up a set of 18" 2002 Carrera 5 spoke lightweight wheels, 18x8 (50mm) with 225/40ZR18's, and 18x10 (65mm) with 285/30ZR18's for my '86 951.
Lots of searching has revealed some information about which spacers to use for fitting the late offset wheels onto an early offset 951.
We can use most 17 and 18 et 50-65 mm with 1 to 1.5 spacers.
Largest wheel fitment without fender modifications: Front 18x9 et 52 with 1“ spacer, Rear 18x11 et 45 some cars may require 1/4" spacer and should require the top shock tower bolt to be reversed. Sounds like I won't have a fitment issue on either end and won't have to reverse the bolt.
Based on this information, I should need 1" spacers for the front and 1.5" spacers for the rear?