Welcome aboard form the wet side. That serial number sounds like about early 76 maybe even late 75. Have you checked out Different's serial numbers in the reference section?
Do you see a Geneseo on the bottom of the barrel near the gas cylinder?
We shoot at the Cascade Rifle and Pistol range in Ravensdale but are always open to try out new ranges. Here's a link to the subforum where our meet info is posted: