833 I.D. help

I just bought an 833, but not sure what it is. It is cast iron case and tail shaft. It does have a large IBR 5.12", and a large yoke 727 style output shaft. It is A-body, and came with complete shifter rods,and handle. on the side mounting pad it has pp833 5439.
I am confused b/c I thought that all OD transmissions were aluminum and had a small 904 style yoke with the 5.12 IBR, and this is cast iron and with a large yoke.
Any thoughts?
Thanks