1979 305 v-8 compression check

I tested my compression today and got 89 to 110 psi in all but one cylinder which registered 0. Does anyone know what the #'s should be and what might cause the 0?

 

When I had my motor built, it had 170 in all the cylinders. What may be causing the zero, is broken rings, or a stuck valve, but the rings are more likely. Either that, or a hole in the piston, a crack in the head, or block. Whatever it is, it won't be an easy fix.<p>~Chuck<p>----------<br>Chuck's Chevy Truck Pages - Snowplowing Central<br>http://members.aol.com/csmith669/plowcentral.html

 

Well, I replaced the heads and remedied that problem. Inherited two smaller problems. Now the oil pressure runs around 15 psi instead of thirty. Not sure what that means or what I should check. Also we replaced the water temp sending unit and now the gauge shows hot all the time, even after new thermostat install. i'm wondering if the sending unit could be faulty or if I should check something else.