Should have a Dana 30 front and a Dana 44 rear. You can usually pick up normal wear parts at almost any auto part store. Other items may need to be picked up at a specialist site or ordered.
Its pretty apparent that your son's buddy doesn't know what he is talking about, since there is no such thing as a Dana 20 front axle (Dana 20Transfer Case , yes) and a Dana 30 is a FRONT axle, not a rear axle...