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the only accurate way to determine comp ratio is to cc the head, using a top plate and graduated cylinder that measures the cc's of fluid you use to fill each combustion chamber. Divide the cc's displacement of the piston and add in the cc's from the gasket clearance and you have the ratio.
In general, Model B heads ( with a giant C on top) are 4.6:1, stock A heads are 4.22:1, The "police head" (with a giant B on top) is 5.22:1, Snyder has a 5.5 and a 6.0 ( the majority are 5.5), Brumfields ran from 5.9 to whatever was special ordered and they have a BF cast on the top of the head. Your odds of finding a used HC head are slim, but there are some around, mostly police heads and Snyder 5.5 heads. The most common have a heart shaped combustion chamber. Winfields came in 3 ratios, determined by the serial number, but they're scarce as hens teeth and very pricey.
link to Vince's page on Ford heads
http://www.fordgarage.com/pages/ABcy...comparison.htm
link to Vince's page on Simmons head
http://www.fordgarage.com/pages/simmonscylinderhead.htm