driveshaft ?

i need to get a driveshaft shortened for my dart. i have several to choose from. i have one from a truck, a newport that stepsdown on one end, and one from a dart that stepsdown as well. which one do i get shortened? i'm going to be running a 340 est.350hp, 727 w/2200 stall and an 8.25 with 3.21 gears. the truck shaft is fairly big in diameter and the other 2 are smaller. i will be shorting one to 48.5 inches. thanks

driveshafts.jpg