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Some basics that should be considered:

1. The cylinder pressures generally decline from front to back. If the engine was a rebuild under the previous owner a less careful machine shop may have milled the block deck out of level with the centerline of the crank. Alternately, the machine shop may have milled the cylinder head surfaces without first checking to see if the finished cc's of the combustion chambers would be as equal as practical.

2. Is the gauge on the compression tester accurate?
If it were mine i would rig up some adapters and check it against "known good" gauges on a stable pressure source like a portable air tank.

3. Borescopes have become remarkable good and relatively inexpensive. The Harbor Freight 9mm diameter head size one made by Autel can slip through a 14mm sparkplug hole and show you whether abnormally high compression readings are due to carbon deposits.

http://www.amazon.com/Autel-AULMV20155-M...gital+borescope

4. The 170 psi reading low cylinder should routinely have a second test after adding two tablespoon sized squirts of 50 weight engine oil to the high side of piston gap in the cylinder and turning over the engine by hand a time or two.
If pressure increases with this "wet test" more than 20 psi there is something wrong with the rings or maybe bore finish or size in that cylinder.

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