John,I have checked some 906 heads and the recess area is about .090-.100 deep stock.One issue is they are not a machined area as you know and some chambers have a bit of slag in them.Another issue is at the point where the recess meets area of the chamber where the valves are.Some appear to be thinner in that area.As I wrote earlier I would rather use a plus deck height than a quench dome.

9.5-1 can be reached,depending on bore size with a closed chamber cyl hd @80cc's. 5 to 7 cc dome (off the top of my head )would allow 10.5-1.That is a very small dome that I have used before (Ross) 4.280 bore 0 deck@9.968 with 84 cc Eddies and 5 cc dome 10.7-1 .040 quench.

I will continue to investigate all the issues discussed. I may have misspoke as I am pretty sure these are lighter than any Diamonds I have used.The important issue is we now have a platform that can be used to cover several combos without the custom prices.