It's a little known fact that if you Google a Chevy block number, you'll get mucho information. Most of these block codes are on the web.

355909 = 305 76-79 Truck
355909 = 305 78-79 Pass,Camaro,Malibu,Monte Carlo,Nova

This same casting number was used on a 1976, 262 C.I. block.

I'm pretty sure that 355909 ended with the 1979 year, and was not used into the 80's - but I could be wrong.

This is a great site:

http://www.mortec.com/location.htm