Nope, you're right. I can't see any evidence that O'Kane sought a right angle to the track. He might have had a preference for angles that were close, but I don't see any evidence for it.
I think you're right about him using the spread input to hit the bow and stern of the target in that instance. Please note that per the Submarine Torpedo Fire Control Manual, this would have been a computed spread of about 80%. He wouldn't have been just fiddling with the spread dial and hoping the setting was good. That would have earned him a good roasting by his friend, Admiral Lockwood, when he got home.
Hey! That's not fair! I use the TDC. It computes my lead angle and dries my oilskins when I come below in bad weather!
