yes a type r crank (ctr or itr) will work in an ls block just remember to get the rods to match the crank, the stroke will change, with the itr it'll change a only a little (ls R/S ratio 1.54, gsr/itr R/S ratio 1.58) the ctr crank and rods combo will give you a big change to 1.84
an ideal r/s...