So some progress tonight! Pulled the valve body and put the spring back in. I also found an error I made when I installed the kit: I put the springs on the wrong side of #52! My trans originally had springs on both sides of #52, I got confused and put the single replacement spring on the "inside" of the piston, not the "outside" facing the retaining plate.

I don't have enough trans fluid to get the level correct... just enough to get to the loop on the bottom of the dipstick. I'll get more fluid tomorrow and report back.

-J