1987 grand am engine noise

looking for a bit of advice. 87 grand am le 3.0 liter fi 6 cyl. with 128k miles
sounds like someone left a wrench in the engine. my first thought was the harmonic balancer. noise comes and goes. but on this model HB is almost solid metal(other thatn a 1/4 inch strip). pulled it and it's very solid(don't know how one on this model would ever go bad with that construction. anyway, had already grabbed a spare for $30 on my way home. so thought i'd put it on anyway. obviously did not fix it or i wouldn't be here. btw, no i am not driving it. or putting any stress on this engine yet. started it up again. no smoke. a good sign. well... maybe but not really. if the oil pump is out. looking at the gauges shows no pressure. then it would make these scary noises as it quickly tears up the engine. next step is to pull the oil pan and check the pump. Also. when revving the engine sometimes the noise will dissipate. but it's intermittant. no correlation to a specific rpm or accel decel.
my questions are.
1. when you look at the pump can you tell it it would be malfunctioning? (can still have scars on the surface and work)
2. what can i tell about the damage done to the engine without spending all the time and money of tearing out the engine and disassembling it? (best guess here is to fix pump and see if it starts blowing smoke, no power, etc.)
3. i thought there was a sensor to shut off the fuel pump if the oil pressure was too low?

not good, sounds like a rod bearing, my advice would be to find another engine, prob faster to change than troubleshoot. 87 3.0? sure its not a 3.1

thanks for the advice. but money is the concern. not time. lots of time to play. :) i'm doing the work myself. not worth paying someone else to fix it on that old of a car. any advice you have on checking it out myself would be greatly appreciated.