318/360 Crank/347 running on Dyno

Didn't know about the LS bore and stroke, but I've always wondered what prompted Mopar to build the 5.7 Hemi with what is virtually a 318 bore (3.92") and a 360 crank (3.58"). Funny that GM ended up with a similar combo, makes me wonder if it has some kind of emissions connection, or if the combination works well together to build decent power without having an overly large motor.