Babi Guling - Balinese Suckling Pig - alternative cuts of pork for it?
The pork fat is what gives the taste, so if you would take a less fatty cut of pork, just use a trusted method of preventing it from drying out and that is larding: 


add most of the pork Babi Gulling filling inside the cut 
smear some pork Babi Gulling filling around the cut
cover the cut with pork belly strips (=bacon) as well
use tooth picks to prevent the pork belly strips to fall off.