Sorry buddy, but you are not going to do it with a socket set and a Haynes manual.
It's not the oil pump, it is the bearings. More then likely the cam bearings are out of the motor.
Now you are there and I am here, but I don't know what was in the motor when they bought it or how many miles is presently on the motor. Who the previous owner was - or what ever.
The old first generation V -8 265 - 400 SBC - you could probably try to replace the oil pump by just dropping down the oil pan and removing the old pump and putting in a new pump.
With the new generation 4.8 / 5.3 - 6.0L - forget it.
BUY a Haynes manual and look at the engine rebuild section and then look at the grocery list of tools needed and then price a new crank kit and a new oil pump and all the gaskets and associated hardware and see if it doesn't come to more then what a used or rebuilt engine costs.
There is no easy way to fix your problem - other then a complete rebuild.