Rattling from top end and Low oil pressure.. Help
 

ok so i dont have alot of money into the car so if i want i can do a swap to a l67 if need be but for now i would like to just get it running, there is a rattling tapping from the top end and a loss of power as well as a low oil pressure light on when the rpms are low, any ideas on what to check first and how to check to see if my lower end is done, the car is a 03 Monte SS with 145k.