Engine swap help
 

Hi. I recently acquired a 1995 Blazer off of a friend. Long story short, the engine was changed out before he bought it and he has no idea what year the engine is. I know next to nothing about cars and engines and whatnot so its been a nightmare trying to figure it out. I know its a 4.3 vortec V6, but other than that i have no idea. I read online you can find a casting number to tell you what engine it is. Does anyone happen to know where that would be located? Or possibly any other way to identify the engine? Thanks so much for the help.