How can you tell the difference in a 350 and a 305,I was told it was on the block behind but below the distributor all i see is a serial # and GM is there a way just by looking to tell the diff.I have an 80 model chevy silverado.  

on my 86 truck it says "GM 5.0L" where you are talking about.  the main way to tell is: if it has a lot of power, its a 350, if it doesn't, its a 305.  i think i am one of the few people to rebuild a 305 instead of throwing it out!

EDIT: give me the serial number and i'll look at my casting # book.  

the best i can make out its 14016379