THIS IS UPDATED FROM LAST NIGHT
According to the 1951 Kaiser & Frazer parts books, the standard crankshaft (p/n 207146, both makes) came with a bushing; the hydra-matic crankshaft (p/n 209227) does not come with the pilot bushing (separate part) and uses a different design flywheel. The same part numbers as listed here seem to be carried through Kaisers into the 1955 model year.
Attached to this is a .pdf file listing engine numbers involved in an attempt by the Detroit Engine Division to rework the standard transmission crankshaft for use in engines set up for the Hydra-Matic. Please read the cover page carefully; you will see that these reworked crankshafts should NOT be used if the engine gets an overhaul or rebuild; replace with the proper part number.
Oh yes, as far as the Service Bulletin indexes go, the dealer & distributor service bulletin Mr. Alexander refers to was never released. This is the only information out of the factory on this subject.