It's the same crank, the tolerances on the front bore are just tighter for a 160, (you can't remove as much material if the bore is corroded on a 160). You won't find out what you have till you overhaul the crank. Basically, if you have a wide deck, when you overhaul, check into it and see if it is feasable finacially for your engine. The performance gain in a 160 is noticeable, more efficiant fuel burn, and there is little if any reliability difference.
I like the 150 in my own Cub, but you must understand that I am a complete freak. I'm a flat lander (which has been pointed out to me, thanks diggler), live where it is useually cool, I fly a lot and cheap gas is important to me, and most importantly my Cub is stripped, (no electrics so I hand prop), and nothing in it it doesn't absolutely need. For me, the narrow deck is lighter than the wide deck, and even at 150, produces all the power I need. Because I'm lighter, I can carry as much (or more)as the higher HP machines and land shorter than them because my gross with the same payload is considerably less. If I had a "normal" Cub, I would definately want the 160.