slant 6 head shave
Doing a little more math I came across this article.
http://www.moparmusclemagazine.com/techarticles/mopp_0602_chrysler_slant_six_engine/index.html
It claims they cut .268 off the head to get approximatly 13:1. Setting up a simple proportion yielded the following; for 10.5 you must cut .216. SOunds like a lot to me.
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