Mike, You probably got one of the last Regular frame guns made. They were making some in the Longrange Wildfowl until about this time, but I guess you could still get/order a Regular frame gun. The Single Sighting Plane was an option in 1939 for $5.00 extra, and became standard in 1940. As far as the "lightening holes", they were probably put there by a previous owner or sent back to the factory and done so. There was a picture posted a while back with what you are describing.