Looks like there is a tapered bearing race still left in your transmission.
AllDataDIY doesn't go into rebuilding the transmission, and I couldn't find an exploded view of the internal parts.
Measure the ID (inside diameter), OD and bearing thickness, and buy a new sealed bearing with those dimensions.
If you find the GM Part number, they will just sell you a bearing, but charge you 10X more for storing it thru GM.