the pistons are usdm type r pistons not jdm this will have a slightly lower ratio i think somewhere around 11.5/1. and deck height on gsr and ls are the same 8.347. stroke difference is ls 3.504 and gsr 3.433, ls has shorter rods though 5.394 compared to 5.429 in gsr. And also using b16 head cause it flows better has better valve angle and not so hard to find intake manifold i like.