Oil pressure please help

I have an original 6 cylinder car with a 360 put in it by the previous owner the oil pressure when it's at idle is around 30 when cruising its around 20 it seems a little low to me so I asked a couple people about it and they said to run 50 weight oil so I did that and when I crank the car up the oil pressure is way better but it sounds like the engine is knocking and it didn't sound like that with regular oil what should the pressure be on any help greatly appreciated