Where would I find the serial number on an engine block?

I recently bought a 72 dart swinger. Its got a 318. I would like to know more about it though since the car was originally a slant 6 car. Can someone tell me where to find this?

Another question for someone to help with...Would the trans or rear end have to be swapped as well for the 318 from the slant 6? I would like to know what tranny it has as well. Anyway to tell? serial numbers on that, etc?

I appreciate the help. I dont have much history on my car and am trying to learn as much as possible.