Trans locked up shifting to second
I am going to bet that your manual valve body is a trango tf3 modified one...... I have seen issues with this kit twice before and will not use them again. The kit causes the transmission to be so sensitive to linkage adjustment (due to the spool valve they supply?) That if everything isn't spot on the transmission could be slightly between gears, which engages two gears at once locking the transmission much like a trans brake. This happened on my friends bb duster (on a gentle 1-2 shift it locked up) and in my 72 swinger (incorrectly adjusted linkage, not fully into park, me standing in front of the car adjusting timing, I opened the throttle to about 2500 rpm and the car jumped the park pawl and launched at me crushing my legs and breaking my right femur).
It was no ones fault but my own, and I learned some valuable lessons and that day. My next 727 will have a proper aftermarket valve body, not one modified with the Transgo kit.
What has been modified in your transmission? Be careful! The sprag (or overrunning clutc) should be checked after any drive line failures or shock. A drum explosion will ruin your day....google 727 drum explode for graphic pics and details.