treefarmer - For your '54 3100, the torque tube setup is what it was equipped with per the
1954 Chevrolet Truck data PDF found in the GM Heritage Center archives. See the screenshot below. Models 3600 and up had open style drive shaft setups. Both setups are shown/described in the Shop Manual and FAM, but are listed for the models numbers applicable.
On the specialty bell housing to adapt the transmission you have, it does bolt up to a SBC and the 1963 and later design in-line 6 engines, but will not bolt up to a 1962 and earlier 235/261 engine. Are you planning an engine swap in addition to the transmission? If so, you will need to definitely make changes in the current rear engine mount/cross member set up to support the change.
Good luck with your project.
