Low Oil Pressure '87 K5 Blazer?
 

From a cold start and idle until warm-up, the oil pressure gauge reads just under "30". But as I drive it, the pressure degrades 'til it reaches "0". Is this normal or something I need to be concerned about?

Depends on whether that is the actual pressure or if there is a problem with the oil pressure sending unit. You need to remove the stock oil pressure sending unit (located on the back of the engine between the driver side valve cover and the distributor) and plumb in a manual oil pressure gauge. If you use a 1/4" T, you can install both. The manual gauge will allow you to verify the accuracy of the stock electronic unit.

If it really is that low, you have a problem.