I replied and by the time I hit submit, it was gone. In short, you can't use the TRW or Unit 500 crank in your cases... as far as I know. The stoke is the same on the TRW but it runs in a timing side bush for starters.
The Unit 500 crank is much shorter on the stroke and up until I believe 1969 they ran in a bush in the timing side as well.
Your best bet is to keep looking for a Pre-Unit crank And also you should have the same size bearings timing and drive side..part number E1591 for a '56 model.
Hope that helps ?