The cylinder compression test gives you the pressure value, in pounds per square inch, that is built up in the cylinder after a couple of sweeps of the piston in the cylinder bore - ie, cranking compression. This info is used to determine basically how well your piston rings and valves are sealing in your engine, and really has nothing to do with the actual final "compression ratio" of your particular combination.
The actual final compression ration of an engine is determined by careful measurement of several areas, including cylinder head volume (measured in cc's), depth of the top of the piston below (or above) the deck, head gasket thickness, deck height, etc. etc. Without knowing all of the variables involved, you can't determine your actual final compression ratio.
If you look on one of the bolts on the rear end housing, you should find a small metal tag with the gear ratio stamped into it. If the diffy has been apart before, the tag will probably be missing and you can do the driveshaft turns thingie to get a very close guess on the ratio. Hope this helps.