Knock with loss of Oil Pressure

Hey guy's got a little question for you all. I have a 82 F-150 w/ a 76 351W from Torino in it. When I bought the truck there were quite a few issues with it. I have fixed most of them but a couple. At times the engine will run fine and then all of a sudden it will be hard to start after it has warmed up. I have done a major tune-up, plugs, cap, carb (new), filters. I am getting 9 psi to the carb. Once it starts it runs great. Just recently it would not start at all. It would start then shut off immediatly. I changed the ECU, did not fix it, then I re-grounded the ECU and it works, along with fixing the hard start. Did I get another bad ECU?
The next question is about a week ago it started knocking from the bottom of the engine, I could not tell oil pressure since my gauges were not working and I installed a proper oil gauge since then. At intial start up I would get 45-54 PSI oil pressure, then it would tapper down as the engine warmed up to about 30. No increase in pressure when engine speed was increaded and it would start knocking, bottom end. I have the lower part of the engine dissasembled at this time and was curious if I should just change the rod bearings or both rod and main? The oil pump seems to be fine, no clogs and guggles when turned. Two of the rod bearing #7 and #6 were silver with just a little copper color left and a lot of scratches with a couple of deep gouges, could this have caused this problem. I have not taken the main bearing off since everything is still connected to the engine and I did not pull it out. I do not know how many miles is on this engine, but everything else looks good. Connecting rods are all tight on the wrist pins with no slope in them? I am just curious as I already have the lower end torn apart is there something else I should look at and change? Any assistance would be appreciated.