Got an update from my mechanic just now. The 60E is out. He set the 80E in to test fit and everything looks good except the driveshaft, which we saw coming. Thanks to everyone here who pointed that out. He's brainstorming some options to make everything work and is going to update me once he's got it figured out. He said whatever we do it's going to have to be shortened for sure. Apparently the yoke on the 80E wasn't exactly what he was expecting to see, either. He asked me to clarify the specs of the donor truck so he could do some more research. Wish I would have taken some better pictures of the yoke side of the 80E before I dropped everything off so I had it to look at. If anyone has any input on the matter feel free to chime in. I told him I'd look into it some more as well and let him know if I figured anything out, but driveline stuff like this is unfamiliar territory for me. I'll probably end up going with whatever solution he feels most comfortable with.
Just out of curiosity... I know a custom driveshaft would be expensive, but that would pretty much eliminate any further complications like conversion U-joints right? Would it be stupid to do something like that now if I'm planning on swapping a 14 bolt SF rear end in down the road? Just throwing some ideas around.