well i got a set of j20 axles from a 79 installed into my j10. i tried all the driveshafts and none of them work. the j10's rear shaft is too long and the j20's is too short. the j10's front is too short and i wasn't able to remove the j20's front shaft yet. looks like i'll be making a trip to the drive shaft shop to get a couple of new shafts made up.
03 GMC 2500HD - DD/toy hauler
06 Street Glide - Cruiser