Sounds like a cool project! Couple additional thoughts:
@Myazel you're correct that the 2.7L RS ran 8.5:1 pistons with early S spec cams. One of the challenges you'd run into is that your CIS pistons don't have the valve clearance for S cams. If you machine them, you'll lower the compression even more than they already are, and wouldn't run well with aggressive cams.
Another consideration is that your cylinders if original, they should be alusil. In case you decide to splurge for some aftermarket pistons, you may need to have your cylinders nikasil plated. I've not heard of using the alusil with aftermarket pistons. Perhaps others can chime in if they've heard differently. There are some off the shelf upgrades at places like EBS that are "reasonable" by Porsche standards but not necessarily cheap.
Sounds like you wouldn't need to tear into the bottom end, but in case you need to, do some research first. The bottom ends on the mag case motors are, ahem, not the most robust. Especially the 2.7L ones since they took some overheating abuse with the emissions equipment. When you disassemble them, the cases tend to warp and need $$$ in machining to get them right again. Just FYI.
Sounds like fun project, and welcome to the slippery slope!
