you absolutely cannot run an ls crank in a gsr w/o custom pistons 2mm is huge. thats 80 thousandths and that will put the piston above the deck. you need to order a custom set of pistons with a raised pin height to bring it back down in the hole. we usually stock these for this setup but dont have any on hand right now. if you decide you want the custom pistons let me know.

by the way you made a mistake in your math. its 2mm not .2mm. thats 80 thousandths.