Fred,
Thanks for the info on the differences between car and truck!
My 58/59 Sales Litterature, Truck Data Books and my 29-59 Parts Book only lists OD for the 55-57 1/2 ton trucks.
The Parts Book even has a foot note for Non-OD 3-speed transmission cases used on "55-59 COMM w/3-speed (cast 3845122), p/n 3707166" to "use through bolts with nuts at two transmission to clutch housing locations". So it looks like the passenger car case was used as the replacement for the trucks.
58/59 date codes could have been warranty/replacement cases.
Mike B
