i have a b18b with gsr piston n rods, can i switch it with ls rods?

Are you asking if you can use LS rods in your LS with GSR pistons?

LS rod on gSr crank

They are not a direct swap.The GSR rods are thinner at the crank end.You would have to narrow the LS rods and use the GSR bearings.The next thing is the LS rods are shorter so the pistons would be way down in the cylinder and would need a custom piston to correct this.
Glenn