Not sure how far you can bring the compression down, but maybe E85 is an option for you as well. That would require an even bigger fuel system over the gasoline system needed for the turbo. 30% more fuel for E85 over gas.
Easy to lower the compression. Buy new pistons and of course they will have to be custom. The Wiesco forged dish pistons in my TT engine have a 34.2cc dish as well as huge valve reliefs that will accept an almost .900" lift cam. The ring land is also thicker as the top ring is held down further from the piston top. So the piston will take more abuse without failure. My compression is right at 9:1 it's 410 CI....
The pistons were over $1300.00 with tool steel pins. Get out your Debit Card!