Really bad main bearings will usually create a deep thudding knocking sound that will be loudest under acceleration load and possibly quiten out when turning at a constant speed.
Collapsed lifters bent push rods and other upper valve train noise gives a rapping sound that sounds out the top of the enginne.
Bad rod bearings are loudest when backing off rpm's on the engine
Bad bearings in general, if the are bad enough to knock will also reduce the oil pressure.
Fill the crank case with 40 WT oil is a good test for bad rod and main bearings because the thicker oil, unless the engine is totally gone, will quieten it down.
If you are running anything lighter than 30 WT in a high mileage engine swap to 30 wt.
A 440 dodge motor I overhauled had bad a bad main bearing and several well worn mains but did not knock, it did have lower than normal oil pressure. Same with a 460 ford.
I would get a stethoscope, to zero in on the sounds, but you have to know what the sounds interpret to.

 

update to the knocking sound.. iv been drive it for a few day trying to tell when its knocking and when its not.. i just did a oil change. 5w-40 with lucas oil stabilizer. The knock is only when the engine starts warming up. and online at idel speed at lights and any speeds below 15 mph. when the engine is cool when i first start it, its fine. it is a rapid knock and from what i can hear its coming from the top of the engine.

 

I had the same problem last year...it only knocked when it warmed up and at idle. i noticed when it warmed up my oil pressure would drop & the knock would start from the top of the engine. In my case it was when i was desludging the engine and my pump screen got clogged. I replaced the screen & oil pump and the pressure returned to normal and the upper knock from the passenger side valve cover went away. my knock was more like a clanking sound then a deep knock. Alot of good info here mentioned above, im just telling you my situation which may not be the same fix as yours. Good luck finding the root cause.