That burned stuff is common as can be (especially without a TP hooked up) and is still what it looks like happened.
The band is even burned, which leads me to believe it was running on low line pressure (everything was slipping)
I think you should continue on the one you have as the rebuild kit has everything needed to replace the burned up stuff except for the inner and outer most thick steel plates in the clutchpacks. (Called pressure plates)
These are the ones against the drum piston, and under the big snap rings that hold the packs in.
I should see those, and I can tell you if they can be run.
Also at some point we need to get into the valve body and see what's been modified, and then you can make the decision on swapping parts with the other trans.
Who knows, you might end up rebuilding that as well.:D