Some education please. How to tell?

Fifth digit is G, I can't see the block, the long tubes are blocking it. However it has the same thin balancer type as the one that was on the 360 I'm building. I knew from a short drive around the block that couldn't be a 318. Thanks guys, I'll have more questions soon I'm sure, I'll try to keep them to the correct forums. Being that it looks thin to me and it's the same as my known 360, what is thin, how thin?