It seemed like it was tight but I bought a metric socket just a little smaller than the normal one I had been using to try to tighten it and was able to get it to go in a little further. Still not quite far enough, so I ended up ever so slightly opening up an already existing hole on the flexplate where the drain plug was hitting, and also grinding down just a bit of the head of the plug. I think that has it solved. I hope to mate the tranny again to the engine in the next couple of days.
Feeling better about the overall situation, I also installed the throttle cable bracket and return springs. This cable, once installed, basically reduces power when you take your foot off the gas and also gives input to the transmission through a kickdown cable so it knows what gear to select. Pics of that later.
