I have mine out ('88 '31)
Mine was glass tabbed on the aft end and had teak brace on the top securing it down.
I think the forward end slides under the hatch lip also.
The main difficulty is that (on mine) it needs to be re-tabbed in place.
Not an issue for me as I have the bilge pump and all out, painted etc so it is already ground down and ready for an epoxy/glass mat tab back in place.
If any one has devised and easier method that allows for removal I'd love to hear it before I mix the goop.