Yelstn,
You are correct about the harmonic balancer going to a flat face in 1953; but, as you state, it is still possible to adapt those trucks to use a crank (but a little more work than adapting a 49-52 truck). It is not possible to adapt a 54/55 A-D truck to use a crank (without serious messing with grill sheet metal).
Denny,
I have a used pre-54 bumper that has a metal-plate attached to the middle bolt. I don't think it looks like the one in your photo but I will check (if I can find it).
