what block do i have?

went to check my casting numbers today was only able to get the front number they read gm318r35140 what block is this the guy who was helping me my sisters husband is a mechanic he says its a GM block iv never heard of a GM 318 could he be reading the G mistaken for a 6? i looked at it and cant really tell, when i bought it the guy said it was a 318 i assumed Chrysler, anything else i can look at that would be give aways, let me know.