The PZ found in the middle of your serial number indicated that your browning light twenty auto-5 shotgun was made by browning in 1981.
Browning.com has sn data under customer service.
This gun was made in 1981 Value is too difficult to be accurate without seeing the gun. Condition which includes the amount of original finish and original configuration will determine value. Auto 5's with poly-chokes, compensators and recoil pads (other than Mag 12's) will reduce value. A rough ball park figure would be $400-$800 range for this gun. Near mint guns and original box will command an extra premium. Recommend taking it to a gun shop for appraisal.