I run a C-6 mated to a Dana 20 transfer case. Yes the angle is tough on this set up. I had to grind some off the T-case yoke to stop the binding there (front D shaft). I had custom shafts made at a tractor/implement shop) Dana 20 case to Dana 35 frot/8.8 rear. If you go this route make sure the C-6 is the 4x4 model. I had to shorten the output shaft to run the adapter (advance adapters, adapter) It came with a new spud shaft for the transfer case. The 2wd C-6 is different (mine is out of a 84 F-150) The transfer case out of the 150 put my front driveshaft hitting the Radius arms. I used a DUFF early bronco 4wd shifter with some mods as well.
Now about the C-6......
They are bulletproof stock. I wheel mine with a 347 Stroker (about 425hp), but they are a HP pig (takes a lot to spin them). I added a B&M Torque Master torque converter to mine and thats it. I have never overheated mine. I use a DUFF V-8 swap radiator with the hook ups for the auto. The starter was another issue altogether. I run a mid 90's truck starter otherwise the stock starter (my engine block is a '69) grounds out on the headers and will just keep on grinding (starting the engine) until it fries itself out. I do have to run a heat shield and header wrap on that side.
They work with a little work, but if I was to do it all again I would hold out for the C-4/Dana 20 combo (they came stock this way in the Bronco/F100 series). If you look at this make sure the Dana 20 is the 4spd version, some came with just 4hi/2hi/N. You want the 4L/4H/2h/N.
I did my swap back in late 99 early 2000, so lots of stuff that is out now wasnt around then, we made it work though.