Compression ratio question

[Ren]

Hi All, I pulled my 912 engine apart to find shims under the rocker stands, a big bore kit, alloy oil cooler with a porsche part number and only one .25 shim under each of the cylinders. The heads have been skimmed and one has no life left to skim out of it which explains the shims under the rockers. How do I work out the correct amount of copper shims under the cylinders to get the compression ratio right. Maestro dvd said get the books arrrrgggg.

Also have an early 911/912 sunroof handle tool if any one needs one or can exchange for 356 one.

I may need a new head so come all ye faithful what ya got.

Dave Ren