You should be able to remove the screw in the middle and it should pull right off.
I had a problem with mine. I hit it with some WD-40 and jiggled it back and forth while pulling until it started to come loose.
I can't recall if the pony crank is the same as a standard crank but if it is, you'll need a special tool. It's essentially a thin piece of metal with a handle, and the business end looks like a "C" misshapen that slips between the handle and door to release a pressure clip. Hopefully I'm making sense. Tool is available at most Mustang venders, if you need assistance ASAP, try an uhholestry shop and to borrow theirs. It takes 1 second to use.
It's been years since I've had a 65, (still have the tool), not sure if there's a modern trick now.
Mid 65-year, Ford switched from the hidden c-clip held units to the units held in place with a screw. I just looked and a book to verify this. The 65 units' screws were not hidden. If you had a 65-screw handle, you would easily see the screw. If it is a totally plain exterior, you have the early c-clip model.