1994 960 camshaft setup, Compression Ratio. Topic is solved

[Stavsig]

Hope you can help me. just bought a 1994 960 with a broken timing belt and found valve have hit pistons so head has to come off. No problem there as I am a Mechanic of sorts. Problem is former owner had cam gears removed as could not locate timing marks on cam gears (still cant).
These cam gears seem to have no marks and can go back on in three positions. How do I reassemble these cams properly after having the heads done? And how much can I shave off the head or do I need to shave to get a 11.5 to 12 to 1 compression ratio? Any additional tips on the head job will be appreciated.