Ken, changing the cilinder head in a L6 is pretty simple. You stated that your engine has 76cc chambers, so what about smaller chambered heads? You can use the desired compression ratio ti run the supercharger with the 76 cc heads, and have the possibility of swapping latter a small chamber head if You quit the supercharger.
I don't know what sizes are available there but as long as there are smaller engines that uses the same head(194, 230 and 250), for sure may have one. Down here we have a head for alcohol engines with 55cc chambers and hardened valve seats. They have the same size on the ports and valves.
