Hi newtriumphowner

I have just been having a look at parts catalogue#7
as you are not sure what gear it is in

and it looks like the camplate can hold the casing on
because of the way it attaches to the selector forks.
You should try and remove the pin (camplate spindle #26)
and release the camplate from the outer case. then remove the outer case and leave the camplate in the box.
This way you should be able to seen what's wrong in the box.
I think this should work for you though I am not familiar with your bike.