1950 Door Lock Cylinder

[DADDIO]

I have been lurking here, but have yet to post. I picked up a '50 five window as a father/son project. Things are going pretty well. But I came across a problem that is probably very simple:
I need to replace the door lock cylinder as I did not get keys with the truck. I can't seem to remove the cyclinder. I see whatlooks like a tab with a pull hole in the door around the lock case. I figured easy enough, just pull it to the front of the truck to release the cylinder and drop in the new one. That thing won't budge! What am I missing? Thanks- Daddio