Glenn,
I think Bill realized the typo...70/90! My specs show 150 psi for this engine, plus or minus 20 psi. There is much controversy surrounding compression tests, their value, the procedure to get real results, and the results themselves.
A typical approach (I think) would be carburetor blocked WOT, several squirts of oil in each cylinder and crank away.
You have a old truck with an old engine (I assume), so you shouldn't expect new readings. In the usual scenario, the test is used to find a problem. Variation between cylinder pressures, as Bill mentioned, is an indication of a problem.
Taking a reading dry, then taking another after injecting oil into the cylinder can help separate ring wear problems from valve problems.
You have another post indicating your pushrods might be bending as they work...this could effect your readings for sure.
I guess the bottom line is the compression test can give you a indication of the wear of the engine (rings). You already know it's old, so this isn't hot news. What the compression test can do better is help you diagnose and pinpoint cylinder/head/valve problems.
Stuart
