I don't know if this helps or not, but on my '51, to remove the side trim on the doors, I had to remove the door panels to unbolt the front and rear retainers, and the rest just popped off after that. I don't really remember what I did to get the rear quarter moldings off, but I seem to think that the rear clip is also a bolt on type that can be accessed from the inside of the trunk. I don't know about the front clip on the quarter trim. You may have to remove the inner upholstery panel. I wouldn't just start prying, because you can put some pretty good warps in the panels if you're not carefiull. I'd take as much apart as I could to see what needs to be done.
Now that I've posted this, someone who knows about '50's will come on and prove me all wrong!
