B18A/B & B18C1 are very different from each other. GSR came with a bunch of nice goodies such as better rod ratio, 9mm rod bolts stock, use of engine girdle, cylinder oil jets, better blance crank, & a supposed better oil pump but Ive never checked into seeing this to be true. Now if you got deep pockets, you can easily exceed GSR limits. but mod for mods a slight avantage goes to the B18C bottoms.