The 409 was only used in big trucks that required a larger engine. The 348 was still used during these years also. The W motor was not ever factory in 1 ton and smaller trucks.
As Steve says, car today do last much longer. One item that adds to the longevity is the use of unleaded gas believe it or not. Lead deposits are very tough on valves. Today it is rare to do a valve job with 60K on a motor.
Don