I calculate 9.6 to 1, maybe slightly more depending on the clean up on the block. I still say you are flirting with disaster. My 350 pinged with 9.6 to 1 with similar quench and that cam advanced two degrees on the timing set. I didn't degree it but will this time, maybe my cam is out of spec. My heads have filled crossover's, not sure if that effects anything, would probably help if anything. If I can find a single piston and rod, I plan on polishing the chambers from 55 to 60CC to get under 9.5 to 1 with better quench, reuse my .028 head gaskets, since only 91 is available here. Let us know what timing you can run on your 408 with 93. I plan on just under 50 total, 20 base, 18 mechanical and 10 vacuum with a 6AL box.