The big end of the gs-r/type R rods have a different size when compared to a b18a/b rod. The big end of the rod have different sizes when they attach to the crank.
For pistons, to get a gs-r/type R/CTR piston onto a b18a/b(non-vtec) rod, you must mill the small end of the b18a/b rod by 0.7mm one either side.
Use your stock LS rods, than mill the small end if you choose to go with any R series piston.