I am thinking the pins are still in the shift collar and hollow tube. They are threaded in the center, you can install a set screw tighten and it will back them out, or take a large drift and knock the hollow shaft thru but you will shear off the pins ( pins that are laying on the bench in pic) and they will need to be replaced with new ones.
if you are that far into this project I would look for any play on the reversible 540/1000 shaft and drive tube. Consider replacing everything to prevent another failure/ leak.