Well, ain't that fun! I expect yours looks something like the one in the diagrams below. The newer L/U ain't built quite the same, so there isn't a shift cam "lost" in the L/U ('cause it's on the end of the shift shaft!), but there is still a clutch spring and cam follower. So, when you pulled the shift assy all the way out, the spring forced the cam follower (plunger) forward and now it's in the way of getting the angled shift cam fully seated in place.
If you'll study the procedure in Tripp's repair thread for setting-up the prop to take pressure off the spring and plunger, you might find that you can get your shifter assy back into the lower unit.
Even though it's different than Tripp's 50hp, the gears still have ramps and the shift clutch will still climb up on the ramp as the prop is positioned. Thereby taking pressure off the spring/pin so you can perhaps push the pin rearwards, out of the way.
At any rate, nothing to lose; if it doesn't work, you're disassembling the L/U!!
HTH..............ed
