To get at the TC, the bellhousing would have to be unbolted from engine, and trans pulled back. Could look for evidence of recent bolt turning on: Bell housing to Engine, Trans rear support at crossmember, shift linkage at trans, and at least one end of the driveshaft would have to been unbolted.
As to the O/D or not O/D, I thought the facts behind the arguement was whether or not the TC lock-up clutch was locked, or not, due to the particular load and conditions.
Example: Heavy load, O/D off (3rd gear), pulling OK, TC lock-up clutch engaged, so no slippage in trans equals less trans heat.
Or: Heavy load, O/D on, if actually in O/D (4th), if TC clutch unlocks to help pull (much more likely due to O/D ratio!), and stays unlocked due to load in this gear, then slippage goes on and on, creates more heat, etc.
Separately, although a lower gear means higher engine RPM, that revving engine has a lighter load than when coupled through the O/D gear.